Content of /storage/.kodi/userdata/advancedsettings.xml should be:
It was - I just quoted the cache bit.
<buffermode>3</buffermode>
is no buffering so removing it should have no effect but I'll try next week.
I'm using an ExFAT partition for data what I want to be accessible in the both OS. I you have some spare small disks, maybe is worth to try it.
I've only tried NTFS and Ext4 so far. ExFAT is supposed to be less robust than NTFS but I'll have a go. The thing that's really baffling me is why I get this on the RPi4 setup but not the RPi3.