Not a cache or DNS issue as far as I can tell, but it’s obviously interesting you are able to reach the instance.
If I open feddit.nl in a web browser and click on the communities tab, none show up.
Same if they decide to shut down
Exactly, which is a continuity issue of course. I know Mastodon administrators can vow to uphold a code of conduct allowing users to migrate after they warn them they want to shut down.
Again, I don’t know what the issue is with feddit.nl (although it might be on my side if you are able to view the communities), but AFAIK you cannot migrate an account on Lemmy.
To make it more illustrative: imagine the administrator(s) of lemmy.ml or lemmy.world decide(s) to quit tomorrow.
It would be a good reason to return to Reddit IMO. What’s the point of decentralization if you’re completely unsure your account is still there tomorrow?