There is nothing in the documentation to indicate that issuing AT+COPS=0 will, “reset the PLMN search” - but this does, in fact, seem to be the case!
For example:
In such a case, it does seem that issuing AT+COPS=0 will, indeed, “reset the PLMN search” - and will allow the module to escape from the “stuck” state!
Can anyone else corroborate this?
Are there any other undocumented side-effects?
I’ve seen a reference to AT+COPS=0 in PLMN Selection and Reselection Application Note, it’s the first FAQ question.
Can you give the specific reference for that - document number, etc?
Can you give a link?
Do you mean this: sierrawireless.com/en/sitec … ev003.ashx 
That is: Document reference WM_DEV_OAT_APN_008; Rev 003; February 11, 2010
So why on earth is that not stated in the AT Commands Reference 
It has now been posted in a FAQ post 
But is still not mentioned in the AT Commands manual
I can relate this issue with Quectel BG77 modem too. I was not able to attach to any operator though AT+QNWINFO command gave network info (LTE Band 13 and Verizon), but AT+COPS? always gave no operator. I tried with resetting the modem, factore restore it but none of it work. Then I tried AT+COPS=0 and it immediately attached to operator.