It sounds like you're using Confluence not Estuary? (because in Estuary you'd go up to power-off, not down). If yes, the place to give feedback to the maintainer of that skin is the Confluence add-on/skin thread in Kodi forums.
Kodi (core code) logic changed between 17 and 18 so the second case isn't something you can control. It's just how (newer) Kodi works now. It's probably just easiest to not-hide played items so they're visible and can be deleted.
It sounds like the HTPC was the browse master and when you reboot it an election is forced and it takes time for the remaining systems to figure out who is now in charge .. and until that happens name resolution is impacted. As the NAS should be always-on you can "Enable Local Master Browser" in Synology SMB settings (advanced tab) and future elections should be avoided (unless you restart the NAS). You might need to "turn it all off and on again" after the change before things settle. ZeroConf doesn't have the same stupid process 
Two methods:
a) Compile your own image with this value changed: https://github.com/libreelec/libreelec.tv/blob/master/distributions/libreelec/options#l203
b) Install using the default image which creates a 512MB partition and then reboot from an Ubuntu (or similar) LiveUSB and use gparted to shrink /storage and then increase the size of the boot partition.
LE images are currently 235MB and much larger full debug development builds fit in a 512MB partition. Generic sizes will drop considerably in LE10 once we remove 2x nvidia driver blobs from the image.
I don't keep track of them all .. but they're all in this section of the forums.
Online docs talk about global limits but I believe you can set them in individual service files too, and /storage/.config/system.d/ allows you to override any of the embedded .service files with your own (stop/disable the embedded service, then enable/start the custom one). LE doesn't allow you to install things to the core OS (everything is inside a read-only squashfs image) so any extra things you added via docker (or things wrapped as Kodi binary add-ons) must be using the persistent /storage area which is writeable so you can make direct changes.
8GB is the normal minimum we quote for any Kodi install (hence the previous CM1/CM3 with 4GB are limiting) but 16GB is probably a better size to have headroom unless you want to experiment with retro gaming or docker in which case the 32GB card might be attractive (and only $5 more).
As the Slice has a solid metal case a heatsink that achieves contact can conduct more heat away, but there's never been an official heatsink that does this - only homebrew designs that users created for themselves, and the extremely exact dimensions required probably need adjusting for the newer chip design. So the easier option is to get the normal stick-on RPi heatsinks and use those. The result is not as efficient, but it's still an improvement on having no heatsink(s) at all, and you can get them from any Pi reseller for $1.50.
There's no generic S805 image but there's a couple of community releases in these forums which you can experiment with .. it'll be a trial and error process to find something that works.
An educated guess is .. you didn't set whitelist entries so everything is running at 60Hz instead of 25/50 or 29.97/59.94.
In Kodi video settings.
I'm not sure it's the reason, but all the Netflix developers are German
Add-on suggestions are best made via the respective add-on support thread in the Kodi forums.
We'll add that to the list of things CE don't understand then. It's a lengthy list.
Long story short .. there's nothing in the logs. For the sake of experimenting please configure things then stop Kodi with "systemctl stop kodi" and then reboot. Is the calibration preserved? .. this should isolate whether it's the multi-year recurring issue of the OS hard-terminating Kodi (because it's taken far too long to shut-down) which can corrupt guisettings.xml and results in a new file on restart. Also useful to know .. do other settings get lost too?
LE supports update from .tar file and .img.gz so it's not a problem.
As a rule LE (the OS) and Kodi are a simple update. The challenge has always been user-install add-ons. The more junk that's installed the greater the likelihood of something having issues. Make a backup and move it off-box and you can always recover things.
We don't support auto-restore from backup on first boot (and have no plans to add it) but in LE 9.0 the first selection on the first-run wizard is a language chooser .. which might help.
Current efforts are not in vain, and while I can't go into details, I don't have concerns about S905X2/D2 support.
