No.. i've mined some emc2 in 2014 (i have the wallet backup) after that i made a break.. So after a while i wanted to try to resynch my wallet using the Excalibur version.. all done.. but the last three weeks make me worried

I've also downloaded the bootstrap and tried to reindex the block.. works also fine.. but when it came to the last 3 weeks.. the same thing..
The same thing happened to me - three weeks, and on two different computers. I have solved the problem renaming the Einsteinium directory (same thing as delete everything, but without actually deleting anything, and of course backuping the wallet) and reinstalled the Excalibur app from scratch. After that, paste the old wallet instead of the new one and relaunch the app and wait for the whole chain to download and sync again. That worked for me. Good luck!