In order to fix this issue, please use a file explorer to go to /ZooperWidget/Fonts, and delete the contents. Go back to Themer, delete the offending theme, then re-apply this theme. The necessary font will be applied, and the theme will appear correctly.
If you did not manually delete the crucial font file, then it is likely that you are using a "clean up" app such as CleanMaster. To avoid this issue from occurring again, please add Themer and ZooperWidget to the app's "task" and "junk" ignore lists.