I had a similar (maybe the same) problem. I closed CS and reopened it with "Run as administrator" (WAG). In this mode, it worked okay. I reopened it as a user, and it works fine. My guess is that there are some uninitialized variables that are preserved after the RAA session. Just a guess. I am assuming you are using V. 2018.
I am experiencing the same problem. The issue is that I have a laptop with 2 dual screen monitors attached (I have the laptop lid closed). The resolution on the main laptop display is much larger that the two dual screen monitors. The Camtasia Studio main application must be looking that the laptop resolution and using that. I cannot get the Camtasia Studio application to resize on the dual screen monitors. It can get it to resize on the main laptop display.