DantagSame happens to me since the beginning of december. Sometimes, after many tries of restarting, cache clearing etc etc, the SIM 1 is working again. But after I put the phone in airplane mode (as I do every night since the first android), at the morning only SIM 2 is working.
Any news here? I noticed same problems problems (sometimes simcard stopped working and needed to restart my phone) a few weeks ago. Today the SIM slot 1 is definitely dead. I tried other Sim cards (working on slot 2). Clearing the cache, restarting the phone.. the system test with the calculator says that, of course, is not working.