LiftMaster Formula 1 intermittent remote control problems

We own four of the LiftMaster Formula 1 openers and none of the remotes are battery-powered. (we use the remotes build into the vehicles)
All of the bulbs in the openers are incandescent and the ones in the garage are CFL and the openers have worked flawlessly for years. Of late mine has been really intermittent. I can be parked underneath the opener and open/close the door using the remote without issue but when I back out it's impossible to close the door even from one foot outside the garage. Then if I leave it open, run an errand and come back X minutes later and accidentally push the remote (on autopilot) it will close the door but then I cannot reopen from the door. Conversely, if I get out of my car, go into the garage and close the door using the hardwired control then come back X minutes later – my remote will open the door. It's very frustrating and confusing.
I might add that it's been exceptionally hot and humid so this problem may be moisture related.
Regardless, this same thing happened several years ago and I called our local dealer – they sold me a hard CB radio-like antenna to replace the wire with. Of course as soon as I had it in hand the problem went away so I haven't installed it yet but after reading these posts I don't think it's going to resolve my problems.
Any ideas? Thanks!