There are various reasons on why you can receive this message. In this article an invalid Acronis client certificate can cause this issue. This was also marked as a bug (PLTFRM-28047) and will probably be solved in the near future. In any case, should you run into this issue and all quota related checks are positive and quota is indeed not exceeded you can remove the certificate to force a reset of the quota statistics.
Remove the Acronis client certificate.
Specified in the section ‘Acronis Cyber Protect Cloud’.
For regular Acronis quota exceeded message check see 'Quota Exceeded' error