ya, got 2,968,555 here too.
A bit ago (year or more) Avast! did some consolidating of the definitions, and reduced the number from over 3,000,000 to under 2,500,000. Caused a bit of a ruckus then and some thought the a/v protection was lesser, not more.
Point in case: Malwarebytes definitions database sizes increase with time, and suddenly get smaller. Impact of this was that this was caused by definitions for much older spyware/malware, was removed, as they may feel it obsolete and not needed anymore; size of downloaded database fluctuates and thus maybe Avast! is doing the same thing here?
Could be normal housekeeping, is all.