Thank you for the signature suggestion, done!Not a Merlin firmware issue. It would help if you added your specific router to a signature ... I had to dig through your past posts to see what router was causing the problem. The RT-AC88U certainly had a few early firmware issues with beta 1 - but as far as I can tell these were sorted in beta 2 released a few days ago.
I assume you have applied beta 2??
Search results on AC88U here ...
https://www.snbforums.com/search/155459/?q=ac88u&t=post&c[thread]=71038&o=date
Initially it appeared that beta 2 resolved my guest network connectivity issues but my work laptop now establishes connection but without internet access. Others are mentioning dropouts on their guest networks also and I'm following carefully for clues.