I have just upgraded my Pi from a 3B to a 3B+. I am using the same cables and memory card, so quite literally a direct in place replacement. No reinstall or config changes at all.
I first tried this on the March release, and have now upgrade to the current 2020-06-03, (Kodi v18.7), and the result is the same.
I do not have an advancedsetting.xml to override anything.
Running on the the 3B, everything was fine, apart from lack of CPU grunt and overheating when playing HEVC.
Now on the 3B+, everything that I play results in constant ‘Buffering’ messages on screen. Swap the 3B back in and all is fine.
Can anyone suggest anything that I can look at to try and fix this?