Just an update.
I did contact Garmin with regards to this issue, but they didn't have any suggestions. Just said if it continues to happen, that I may have to send the unit in to be looked at.
As mentioned previously, I do have a Scala intercomm system. Yesterday while riding, I encountered the frequent loss of satellite reception messages and odd tracking lines on the GPS (Montana 650t) over a 2 hour stent, as described earlier.
I turned the Scala Rider off while riding and behold, perfect tracking and no loss of of reception with the GPS performing beautifully for 1-1/2 hours. It seems the ScalaRider is in some way causing the interference problem.
I do have the Scala Rider "bluetoothed" to my Samsung Android phone.
I may try to remove the BT connection and test it again to see if the BT is causing the problem by itself. I am not optimistic with this, though as other Garmin products run BT successfully.
Any one else running a Scala Rider G9 with a Montana 6XX successfully?