Just an observation from copying custom maps over from my Fenix 5X
- initially the 955 wasn't recognised (Windows 10); I solved this by selecting the device manually as "MTP device"
- I copied over my four custom KMZ maps from the Fenix 5X and only two of them worked. After a while wondering, I tried renaming them as I noticed the two which had failed had longer filenames. With shorter names they seem to work fine.