Huawei Y9 Intermittently not recognising SIM Cards

My Huawei Y9 has recently started to intermittently stop recognising either SIM card in the dual sim slots. Once this happens I can restart the phone or set to aeroplane mode for a number of minutes and this usually resolves it for a short period before the exclamation comes again in place of the mobile reception.
I have confident of both SIM cards functioning well as I have tried them in another phone, and also tried a different SIM card in my phone and the error occurred again. So I am sure that the issue is with the phone.
I have followed the following steps but to no avail:
Restarting phone
Removing SIM cards
Checking other SIM cards
Running in Safe Mode
Clearing Android Cache via Recovery mode
Reset Network settings
Checked for IMEI (It is there when the card is working, and null when it isn't)
Have the latest updates installed

Other than a factory reset (which I don't want to do until I have exhausted all options), I am not sure what to do. The phone is only six months old and still under warranty, however it was bought in Cambodia and I am now living in Brazil so I don't think they have service options readily available here.

Any suggestions?

Welcome to Android Central! There could be a problem with the SIM reader. Use a can of compressed air to blow out the SIM slot, and (if possible), a Q-tip dipped in rubbing alcohol to clean the contacts.