Okay I see the same for me, so it is buggy Curl (oh surprise) or there are too many connections to tvh (i don't think so).
I use a extern Tvh server and got the same problem so it is not LE-Tvh build related.
The easiest way to check for Curl problem is to update to a milhouse build and check if it is working there (I curently have no time to switch one of my test units).
At least you can reproduce it, that means I'm not mad or having paranormal issues 
Don't think it's too many connections either, curl just appears to try to reuse them, with max 15 connections apparently (same on windows kodi), but on LE something just goes wrong and they stall until timeout... causing the annoying 10 sec. delays 
I will try to report the non standard HEAD returning contents to TVH guys, maybe that actually fixes it...
I'm having the issue since OE6 at least, then it's not new at all, I may try LE8 / milhouse soon out of curiosity.
Thanks CvH for all your help, testing and confirming the problem!
curl is the culprit of so much problems due the fact that every "server" reacts a bit different and curl isn't know for his rock solid releases 
best try milhouse he has some new version - maybe it is already fixed maybe not 
oh goush ... find the problem
anyone interested in bisecting curl ?
nars maybe you open an issue at the curl tracker ? Issues · curl/curl · GitHub
its a bit useless to dig into it because we have too less understanding of the code
imagecache: handle HTTP HEAD request correctly (no payload) · tvheadend/tvheadend@04e1190 · GitHub
v4.1.2214 - lets have a look if the builds are done if this work or not
I did tried your build 4.1-2216-30.08.2016 and it seems perfect now! 
Btw, just out of curiosity you have any idea if it will also be fixed on tvh 4.0.x? (my interest is that I still use it on my main tvh server, but I will eventually upgrade it anyway...)
Many thanks for your help and all the ones involved.
4.0 is dead and has a lot problems - so "stable" isn't the word you are searching for
but not saying Tvh 4.1... has no problems - it has still an undiscovered mem leak which consumes all ram at the host -> dead lock (restart every night fixes it for me)
4.0 is stable for me, missing some new features... but usually no problems running for months on my main server... but yes I will eventually upgrade it for sure.
Anyway I could then see on git that the fix was also applied on 4.0 branch (along with some few other commits since 4.0.9) then maybe not fully dead yet, unless it is for you and you will not compile updated addon
damn it 
so i have to update it ;D
It's back with
Server : HTS Tvheadend 4.1.2415
Client 3,4,14 kodi 17, libreelec beta 3.
.11:03:32.596 T:140608927053568 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/520
11:03:32.596 T:140608759957248 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/575
11:03:32.628 T:140610540812416 NOTICE: CVideoPlayer::CloseFile()
11:03:32.628 T:140610540812416 NOTICE: VideoPlayer: waiting for threads to exit
11:03:32.628 T:140610540812416 NOTICE: VideoPlayer: finished waiting
11:03:32.628 T:140610540812416 NOTICE: CVideoPlayer::CloseFile()
11:03:32.628 T:140610540812416 NOTICE: VideoPlayer: waiting for threads to exit
11:03:32.628 T:140610540812416 NOTICE: VideoPlayer: finished waiting
11:03:39.589 T:140609754248960 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/571
11:03:39.590 T:140609544066816 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/572
11:03:39.590 T:140608927053568 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/570
11:03:39.592 T:140608759957248 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/575
11:03:39.596 T:140609544066816 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/574
11:03:39.597 T:140609754248960 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/573
11:03:39.597 T:140608759957248 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/583
11:03:39.597 T:140608927053568 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/556
11:03:39.600 T:140609544066816 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/547
11:03:39.600 T:140609754248960 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/563
11:03:39.600 T:140608759957248 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/539
11:03:39.601 T:140608927053568 ERROR: CCurlFile::Stat - Failed: HTTP response code said error(22) for http://USERNAME:[email protected]:9981/imagecache/542
11:03:40.466 T:140610540812416 NOTICE: VideoPlayer: Opening: pvr://channels/tv/All channels/pvr.hts2_1707326851.pvr
11:03:40.466 T:140610540812416 WARNING: CDVDMessageQueue(player)::Put MSGQ_NOT_INITIALIZED
Not the same problem... sure you have all ok with tvheadend access control permissions? Maybe it needs some specific permission to get icons, that you didn't enable for that user?If you don't find why try this on ssh and post the output:
Codecurl -o /dev/null -v -m 10 http://USERNAME:[email protected]:9981/imagecache/573
(replace USERNAME/PASSWORD by the same one you use on kodi tvheadend pvr addon...)
Connected to 192.168.1.9 (192.168.1.9) port 9981 (#0)
* Server auth using Basic with user 'admin'
> GET /imagecache/573 HTTP/1.1
> Host: 192.168.1.9:9981
> Authorization: Basic YWRtaW46TWVuc3F1YWQ4OA==
> User-Agent: curl/7.52.0
> Accept: */*
>
< HTTP/1.1 401 Unauthorized
< Server: HTS/tvheadend
< Cache-Control: no-cache
< WWW-Authenticate: Digest realm="tvheadend", qop="auth", nonce="9065e0d12396562 865854e0a510371c0", opaque="9ebf5b2670ed0c0a89f0c91d8dd4723f"
< Connection: Keep-Alive
< Content-Type: text/html
< Content-Length: 193
<
{ [193 bytes data]
* Curl_http_done: called premature == 0
100 193 100 193 0 0 21468 0 --:--:-- --:--:-- --:--:-- 24125
* Connection #0 to host 192.168.1.9 left intactThe thing is,
With the android htsp client it is no problem, in a browser it's not a problem.
The password in client is all good, otherwise I also wouldnt see the stream. And I use the admin login for the client, so let's say with superpowers
Since it works with other client (android Tvheadend htsp client) it's probably something in my pvr.hts client ..... but I 've checked all options and I dont see what else I can do.