Quite a strange thing Ossaio!
I think you need to set up the Expert Advisors again, make sure the lots are correct, and they are placed on single charts. There must be a reason.
Also, if all is good with you, it could be really from the broker. No idea why! Just place the very same EAs on a Demo account with other broker and see if this will happen or not. If it does not, it is from the broker.