Hello, I have to say that I am having the same problem in the "Convert" function. Only 22 minutes converts in some cases or 32 minutes in other cases. A 2-hour video was only converted 24 minutes. Another 50 minute video was converted to 32 minutes.
In 2015 I bought Toast 14, which always worked perfectly, although as the Mac operating system was updated, especially from High Sierra, conversions became a little slower, and with Mojave the application started to crash, reason why the conversions became complicated, so much so that after several attempts with interruptions of the conversion process, the conversion was finally completed. However, the system once warned that the software was not 100% compatible with Mojave, and with Catalina it would no longer work.
For that reason, I upgraded from Toast 14 to Toast 18, but now I am having the problem of truncated conversions.
This deserves a complaint as it is not acceptable for this to happen.