Hi there, I've got a very strange problem I can't fix on my own 
Running LE 7.0.3 on RPi3. I added a TSOP4838 as IR receiver on gpio 18 using lirc_rpi. All working well. I had VNSI client aiming to my remote VDR server. As I wanted to be able to record and view TV at the same time, I needed to add a second DVB-S receiver. This one, a TT-S3600, I connected to my RPi3 client, as I have only one sat cable at my server.
Ok, went and added vdr.backend addon, configured, added channels.conf from server (for to have same channel mapping), set VNSI to localhost instead of my server's address and rebooted.
So far, so good.
Problem now is:
If vdr.backend is running, the IR remote is lagging and keys are not received, so not sent!?
GUI is still responsive and I'm able to control kodi very fast with BT keyboard, but not with remote?
irw gives results, if keys are receipt. But they aren't receipt as they should!
Deactivating vdr.backend gives back full control with IR!
Thought of the USB receiver has its own IR receiver (rc_tt_1500) and tried to disable it, but I can't.
If I 'modprobe - r rc_tt_1500', I get a kernel oops, so no chance this way. 'modinfo dvb_usb_pctv452e' even has no param regarding IR, so I'm lost here.
Added '--lirc=/dev/null' to vdr.start to no avail either 
Don't know what's interfering here...
Last I tried, as it felt like IRQ troubles, was to change TSOP from GPIO 18 to 22 (with corresponding changes to config.txt). Again, without vdr.backend (disabled), remote is working fine. With vdr.backend enabled, the remote is suddenly laggy, unresponsive and sometimes multiple keypresses aren't even recognized (seen with irw).
Switching USB ports didn't helped either.
So, what am I supposed to do, to get this beast pinned down? 
P. S. Stumbled upon this one:
LIRC Remote Not Responding · Issue #246 · hyperion-project/hyperion · GitHub
It matters hyperion, but symptoms are quite identical!