Chiang Mai Immigration - online reservation system appears to be barely working (unless somehow someone else is booking all available slots instantaneously as they become available or something). 

 

They are not answering the phone and there is no phone messaging or anything, it just stops ringing.

 

Can you make a reservation as a walk-in? I'm willing to go there and manually make a future reservation.

 

It worked for me. I booked online on Jan 10 for Feb 8, yesterday I was processed impeccably.

I waited longer than usual but that's because I arrived 40 min too early.  the actual processing time was 20 min from picture to passport. I had all documents and copies ready (retirement).

 

It's true that there are very few slots available each month, I suspect much less than those of us who want to use them. The reason why they are few, or why the phone stops ringing, will be clear to you once you set foor inside the Imm building. They are simply overloaded, although the staff is quite large.

OK, can't help with CM, and don't know if the following applies there. But this does for Bangkok, and should be useful for residents there viewing this topic. (And perhaps other offices? But always check for your locale.)

 

Appointment slots for the online appointment system become available a month in advance.

 

Since the time of the online appointment system's resumption, as it was either shut or went down for a while from a couple years back (covid), the number of retirement extension appointments per day was reduced.  There are only six per day, I believe. So it's a good idea to book ahead early if you want to get in at a preferred date/time.