thankfully its never happened although i've been told that my comic (past iteration) was 'homestuck but better'
now i jokingly refer to it as 'steven universe on adult swim'
to me, it is what it is, although i'm lucky i haven't had any actual criticisms like that hurled at me, so i may be biased, but the fear is always there. i just handle it by taking it in stride and controlling the situation myself.
When in doubt, call it the better version of what they're telling you its copying.
(or, if you had the idea long in advance, might as well say the other work in question owes you some royalties for stealing your ideas.