It sounds as if your fobs may be different than those in the U.S. Do you
have a key lock, or must you unlock by transmitter only?
As far as interference, it's quite possible. The radio frequencies these
systems operate on in the U.S. are actually allocated to military. If
we're particularly near a military installation, car remotes, garage door
openers, and many items don't work intermittently. In fact, many radio
transmissions, if strong enough, can cause interference.
Your remotes may be rolling-code type. I don't believe Hyundai uses those
in the U.S., but other manufacturers do. It is possible in that case for
the transmitter to become unsynchronized with the receiver in the car.
The fudge method you describe sounds like the typical method for
resynchronization of rolling code transmitters.
It sounds to me like the repair facility there is on the right track. If
replacing the transmitter or transmitter battery solves the issue, then I
suspect the issue was present and clear at the time of servicing. If you
indeed have the rolling code type transmitters, then that would
significantly reduce the probability of a BCM error causing
unsynchronization. In fact, I believe the synchronization is not retained
in BCM if battery power is disconnected (presuming your system to be
similar to others of the rolling code type I've seen).