I am trying to find out a similar thing: Working remotely for a self-owned foreign company without an office in Taiwan - legal?
Not sure if it’s really legal - the „right“ way would probably be starting a branch office in Taiwan. Or using a „PEO“ (which charges about 15% of your salary), but provides you with a local employer.
On a related note, I just received my passport submission note today 
Submitted my additional documents on 07/20 - so exactly three weeks of professional review this time. Hope the others still waiting will also receive a response soon!