No - it's not normal. First thing I would do is connect it to your computer, and then delete the "system" folder on the internal drive. Don't worry - it regenerates. Then eject the player, disconnect and reboot. If that doesn't fix it - maybe you need to check your media tags. I've got mine stripped down to bare basics. Sometimes an erroneous tag can play havoc with the database, and because it always scans the cards on boot-up, this could lead to freezes when folder browsing.
If you want a fool proof method - and don't mind just playing in folder view (which is what I do a lot of the time now) - simply duplicate your music (from your main PC library), then on the duplicate copy - remove all tags. Mine is sorted in folders : Artist > Album > Song. The song titles always start with the track number and title - EG Led Zeppelin > Mothership > 13 Stairway To Heaven. Unfortunately this kills sorting via the database - but it does solve a lot of the possible hassles with freezing etc.
This is how I run (amnd the reason I know both ways work) ......
I have one 64Gb card with my entire collection in aac256 (all tagless), then I have a second card with my most used albums all in redbook flac (all tagged).
Both methods work for me - but I did spend quite a bit of time meticulously tagging everything on the FLAC card.
Good luck. Can still be a fickle player (software) - but I keep it simply because once you're playing - nothing else really matters