Laos is never a problem, although I've only ever used Chong Mek when kicking the OA out for its second year. They even let me without the silly health insurance. They're cool
I think it all depends on location and who you strike on the day. The silly border at Poiphet has been refusing 45-day exempts, and sending people to Siam Reap to get TR visa and to fly in. So a mini-van company in Pattaya has jumped in on the show and is now do border runs to Poiphet guaranteeing a new stamp. Now I wonder how that's working? 🤣
Legally you're required, but as others have said, as there will be no interaction with any immigration office it's a waste of time. When they leave Thailand, immigration most definitely won't be asking to see a TM30
Whilst your visa remains active that's what you will enter on. If you are on an extension but do not buy a re-entry permit, you can enter on visa exempt basis