(Some) music not playing on (some) players

Hey all,

I've been reading posts on this forum for some time since I started using LMS, and I'm impressed by all the help & knowledge provided on this forum!
Unfortunately, I have a need for a help thread myself since yesterday.

I've installed the latest LMS 8.0 build on my Synology DS212+, which installed just fine. I can see my music files in the library, and I've setup the Youtube plugin as well.
I can play music from YouTube fine on my Google Mini Nest (using the chromecast bridge plugin), but when I try to play the same music on my RPi-squeezelite the songs just keep skipping immediately. I've checked the logs, I can't find anything going wrong in the YouTube plugin logging. I see the same symptom when playing music files from the NAS itself. When playing a radio stream, it plays fine on the squeezelite player.
The NAS resources are not 100%, but when trying to play a YouTube-stream I can see that the NAS is (at least trying to) processing the stream (+- 150 kb/s download, cpu goes up to 80%, memory usage increases).

I suspect the NAS is having an issue with certain filetypes or the like, but I don't have enough knowledge on LMS to figure out what is going on. Is there anybody that can give me some clues as to what could be wrong?
I'm happy to provide any information that could help with figuring this out.

Thanks in advance!!!