My 910 often loses sat signal during ow swim but has always picked up again once out of the water.
I have 'time of day' set up on one of the data screens for bike and run so I don't have to calculate how much time I have left to cutoffs. I can usually remember that bike cut off is 4pm and the run 11pm (or whatever) so all I have to do is scroll to time of day screen and I can easily see how much time I've got left
How tightly do you hold your handlebars? If you're hanging on for grim death that could be a factor; tension in your lower arms can cause tightness in shoulders/neck as well as magnifying vibrations from the road.