Problems reading SIM Cards

Hello I’m from a little town in Uruguay.

We have a NOVA246 with a 120° sector, it worked perfectly except for a problem reading SIM Cards in my CPEs EG8013C (Atom OD6)

I install my CPEs with their SIM card as it comes from the factory and after a few days my clients complain to me that they do not have service.

I go and you just have to clean the Simcard with an eraser + isopropyl alcohol, very carefully not to leave any residue, and the connection works again.

But a few days later the same problem occurs again.

I have more than 50 clients and it happens regularly with 5-6 clients a month (almost 10%)

Any suggestions? Thank you Ismael