I have a similar throttling probem. Using a PilotAware Rosetta and supplied cable, and Anker 20100 (all about one year old). Under "Status" on the home page I have consistantly "Voltage=Error Frequency =OK Throttle=Throttled". The unit seems to be working OK and the Wi-fi seems stable, the software has just been updated to "version = 20190621". I have changed the GPS dongle for a remote U-Blox-8, which has a much better reception even indoors, although I did put the original U-Blox-7 back in to test, but the status message on the throttling remails the same.
Can someone let me know if this throttling is a reason for concern, and if so how to remedy it?