Your GPU is running really hot, It shouldn't go past 70. Most stress tests pust a 1050Ti to 68 max. You said it's running at 80C.... This also explains the bad frame drops.
Here's what's happening:
When your card is cold or at optimal temperature, your graphics card speed (clock speed) is pushed to the maximum to give you the best performance. Once the GPU is under load (playing games) and reaches a certain high temperature, the GPU speed is decreased automatically in steps, to allow your card to cool down resulting in bad fps during this period. Once your card cools down, the speed is pushed to the maximum again, and this process is repeated. This is managed by NVidia's GPU Boost Technology.
Since your GPU cooling is over heating, you get occasional bad performance. Once you turn the PC on after leaving it to cool down, you will get good performance again until it heats up again.
If your card is under warranty (Usually 3 years so it should be) I suggest you get it replaced and don't tamper with it. If for some reason, it's not under warranty, replace the thermal paste on the card (this will void your warranty). It could also be your PSU as it directly affect your rig's cooling. But your processor doesn't seem to be running too hot so it must be the GPU.
Hope this helped