Our Ecuador distributor Allien GNSS, https://www.allien-gnss.com/, tells us the older 2020.11.09 S100 firmware works better with REGME-IP. S100 can be restored to the older firmware following below tutorial video. Note that the S100 firmware need to be unzipped into .bin file beforehand in order to use GNSS Viewer to load.
GNSS Viewer program:
If later wish to restore S100 back to latest firmware version, can simply follow S100 User Guide section 6-2 procedure.