GPS not working

Hello I am having GPS issues with both my 1040 and 1050 with altitude gradient. Many times I am getting negative gradient even though I am climbing at 12% grade. to correct I need to stop and turn off the GPS within the activity profile and then back on again (it does not matter which GPS system I use, the problem happens with all different GPS) and then back on again. That fixes but only temporarily sometimes it starts acting again whiten the same run sometime on a new activity. I am located in northern Italy (Dolomites). Thank you