Hi,
I've also had the Kemper lock up reading or formatting a USB stick. A Power cycle does fix it for me. As for Rig Manager issues, I haven't had any but I'm sure it exists.
I don't know your amp tastes but my current favorites are Live Ready https://livereadysound.com/ specifically the '79 2204, and Nick K's https://nickkprofiles.bigcartel.com/ JMP.
It took me awhile to adjust to having to buy 3rd party profiles but that is the nature of the beast . There's incredible amps on the Rig Exchange like Feck's 3Monkeys Orangutan but it has grown so large with no curation that it would take days or weeks to go through. After an hour searching my ears are tired and I don't want to play.
I hope you can find some inspiring sounds like I have, though I understand it's a pretty huge search with Kemper. It is far from plug n' play to really get /that/ sound in your head. Once you do it's entirely worth it!
p.s. the lack of an official editor over USB REALLY sucks! Almost a no go return for me when I first got it but the sounds are so good.