Installing EA in MT5 (Mac) suddenly does not work anymore

I usually load a new EA in *mq5-format into the data folder MQL5->Experts, re-start MT5 (Mac) and then an additional *ex5-file will be created and the EA is appearing.

From one day to another this way does not work anymore. When I insert the *mq5-file nothing happens. It will not be compiled to an *ex5-file automatically anymore. Therefore the EA does not appear in MT5.

Does anybody from you knows the reason?

I want to repair my MT5 to exclude that there are other bugs, too.

Thanks for your help in advance.