I don’t know about Laos but I had all the CAAT requirements to go to Yangon this morning and they didn’t let me board. Said things have changed as of today. Hope you get better luck
I'm in the same boat. This is what I have found out so far: Ban Laem border crossing is still open but tomorrow is the last day. You can fly DMK to Siem Reap but they won't allow you to return the same day - as it's too late to fly there today, doing it tomorrow and coming back the next day will push you past the 22nd March certificate/insurance deadline. I've been told you CAN fly to Yangon and back in the same day, but need a Myanmar evisa before going which can take 1-3 days to approve. All 3 are a risk...I'm probably going to try the land crossing tomorrow morning 5am from Ekkamai bus station. Good luck