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It is a problem, you are thrashing good tasks which have to be resent then, wasting resources. In your Primegrid account, choose to receive only PPS Sieve tasks and you'll be fine.
And change the title of this post, if it's not too much inconvenience, because cheating is an ugly word, usually associated with FUD and everything is working as it should in this case.

You should look for answers / ask on PrimeGrid forums. It's better not to get errors.