/13/thailand-greenlights-income-tax-exemption-for-investment-token-earnings-report/ If I have interpreted this correctly the new exemptions started January 1st this year. used to be taxed.
I know someone who also does this as a FIFO worker and was eventually told that they couldn't continuously do it. He then applied for an education visa which covered him for 15 months. Like everything in Thailand maybe it depends on what government bureaucrat you end up with.