Will I face issues applying for a DTV in Vietnam if my work permit expires before my Non-B visa?

Once your reason to stay in Thailand ends, (work) so does your permission to stay. You also need a cancellation letter from your employer to get the work permit cancelled at DOL, and then take it to immigration to cancel your visa. You can do this in advance.

As my knowledge, the visa automatically expires once the work permit does, technically. But they sometimes doesn’t find out. But if you don’t wanna face later visa complications, you better cancel you visa at the immigration with your work permit cancellation letter provided from your work. And better to go out before Aug 1st.

In my case, I didn’t cancel my work permit and my visa was still opening when I left out the country and I didn’t pay any overstaying fees but later I was coming in again with different visa, that opening date was an issue