If you can replicate the problem riding with the Tacx app that would narrow it down to the trainer itself so you could raise it with Garmin support. This was discussed in a previous thread but there wasn’t a clear solution. If you want to rule out overheating, aim a fan at the trainer and see if it changes anything. You could also try riding at a higher cadence and see if that helps. High power, low cadence, and high resistance (higher Trainer Difficulty on a climb) will tend to bring out any overheating issues.