I would say about 80% of my Venus flytraps do this each summer. Plus it's more the outer Edge venus fly traps what is more affected in Mid summer.
I use rain water only, plus shamrock peat moss and horticultural perlite only at 50/50 mix, I have noticed the thermometer in the greenhouse has hit 47 degrees over the last few weeks, as the greenhouse is in full sun from morning till sunset.