undercoating should not have changed anything...is it safe to assume that you were previously able to remote start it successfully over the same distance previously?
If so, and just throwing this out there - Recently I bought a 4-pack of the energizer cr-2032's (the car fobs as well as our tv remotes all use them)....swapped one into the TV remote, and it was still acting dead (really short range)....turned out that in that pack of 4, 2 of them tested out at 2.7V instead of 3...

 

Have you tried it someplace else? E.g. if you always remote start it in your driveway or in the same parking lot, take it somewhere else and try.

Odds are it's some local interference...maybe somebody put up a new access point or other radio/telecom equipment (I don't know the frequency these transmitters use...).

You FOB may also be damaged internally...there are antennas, and if somebody put some weight on the FOB it might have damaged the internal antenna.

 

Good point. Local interference can happen, especially in parking lots.

 

I recently started having distance issues with the remote
the issue was with the contacts - some crud has built up on gold side
a quick wipe with a q-tip and it works well again