FYI:
This information only concern people with both ROC (Taiwan) passport and work permit.
When I first applied for work permit in June 2016, my nationality was changed from TAIWAN to CHINA by Labor office. When I objected, the Chiang Mai labor office said that since there is the word "CHINA" on my passport, I am Chinese. This caused me and my agent to change all the mentions of Taiwanese to Chinese on visa application.
Having applied for extension as Chinese three times, this year, my application was not accepted because the correct name is "CHINA TAIWAN". I was told to sent my work permit and letter from city government back to appropriate office for correction. According to the officer at Immigration Office, there were multiple inter-agency meetings on this matter. It is "CHINA TAIWAN".
TLDR : Answer Summary
This post discusses the issues faced by ROC (Taiwan) passport holders regarding their nationality classification on work permits in Thailand. It highlights a situation where the Chiang Mai labor office incorrectly classified a Taiwan national as Chinese due to the wording on their passport, leading to complications in visa applications and extensions. The correct designation, as per recent findings, is "CHINA TAIWAN," which should be reflected in all official documents.