I have two separate 1st gen SE phones that started to get the "No SIM" error within days of each other. Is there a known issue with the latest software update that might be causing the problem? I have been able to get the SIM to be recognized by turning off/on, but now even that is failing.
iPhone SE
It sounds like a bad connection between SIM card and phone. Try wiping your SIM card with a dry microfiber cloth. If it did not make a difference, contact your Carrier and ask for a new SIM card. If it does not make a difference either, then you should hand over your iPhone to an authorized repair shop and have them look at it.
You can read more about iPhone Repair and Service here:
iPhone Repair - Official Apple Support
No SIM error
