Currently, I haven't seen this problem before in my machine (my Chitubox version is 1.8.1), please upload the log file for us to locating the bug asap.
Before the reason was found, you can try to reset Chitubox to factory setting by clicking Menu -> Help -> Factory Setting
And if it doesn't solve the problem, try to delete all files and folders under the Chitubox log path.
The log path is
C:\Users\your-user-name\AppData\Local\ChiTuBox
The folder can also be opened by clicking Menu -> Help -> Open Log Path