I used powerlines with LibreElec for many years.
In the early days I used x86 systems, which I allowed to sleep when inactive. A common problem was that they would wake up without internet connection. LibreElec displayed a private IP address.
My diagnosis was that the powerline entered it's own sleep mode, and when the LibreElec system woke, the powerline did not wake fast enough, so LibreElec resumed with no internet connectivity and did not understand to try again after a couple of seconds. Pulling and inserting the ethernet cable usually fixed it, or doing a reboot.
When I moved away from x86 to RPi the problem no longer manifested since the Pi was running 24/7. It still happens sometimes if everything is powered down and back up (for maintenance) or after a power cut but for me this is very rare so I don't worry
This is not identical to your problem but maybe it gives you some things to check.
The commonality is that
1. Powerline sometimes drops or takes a couple of seconds to respond after sleeping
2. LibreElec doesn't recover automatically if the initial ethernet connection is broken
FYI most powerline have a utility to disable sleep mode.