Hello, I reported this problem in a post in January: Max Transit Duo Pro does not archive 7 days of GPS data but only one. I opened a ticket for this bug.
According to the ticket this should be solved with the next firmware release. On Thursday I installed the Firmware 8.5.2 Beta 1 and it solved the problem. Right now I have already 4 days of GPS data. Unfortunately this bug is not mentioned in the corresponding Release Notes.
Maybe this beta version of the firmware solves the problem for your hardware as well?