Bending/melting is depends on the qulaity of the PCR tube using.

Even for me also sometimes tubes bend for the heat. Reaction working depends on Primer annealing to DNA, not based on your tube melting. That means when you are using strong tubes TA is not suitable to anneal the Primer to templet DNA so your reaction not working. Then you change TA and try, otherwise check/set the reaction using Gradient.

Axygen PCR tubes are standard and never melt.

Good Luck!!!

I suspect that the tubes that melt are thinner plastic. This means that the reaction mix reaches the correct temperatures quite quickly. If one temperature is on the verge of working/not working then the thicker tube may be slowing the heating of the sample ( or the cooling) so that the cycle never actually reaches the temperature that you set on the pcr machine. It is a bit like having too large a reaction volume....it may not all reach 94 or the Ta of the primers. If you want the thicker tubes to work then try increasing the times at 95c and also 61c to make sure that the reaction mix does actually reach both 95 on the way up and also 61 on the way down during cycling

It is also worth checking the PCR machine. Some old pcr machines were customised at a 50ul reaction mix and may have problems at smaller sample sizes. If your pcr machine has very fast ramp rates between temperatures then set a slower ramp rate for this experiment

Have you checked the Q5 protocol from NEB, the Denaturation is 98oc, not 95oc.