sometimes things happens because the people at the checkin desk do not now the last rules. Believe it is NOT swiss air but the person, not well informed at the checkin desk. Just ask for the superior!
But if it is not a muli entry visa you have to buy a re entry permit. Can buy that at the airport in a part of the "room"where you queue is a small office where you can get that re entry permit.
depend on the visa. Have a look. If it says"multi entry"then you just leave thailand and return without problems. Of course now a days you have to apply for COE etc etc.
Christmas this year, 2020?? forget it.just forget it. Maybe you have heard about corona, two weeks quarantaine and lots of paperwork. Absolute impossible.