How do I prevent a proofreading tool from introducing errors into my text?

Proofreading introduces errors. The proofreading tool mostly finds missing commas. But it also introduces gross errors into my text. I have not used this tool for months because of this and hoped it would have been fixed. Here are a couple of examples:

 "When COVID-19 paWhen theic arrived, the audience was not allowed to congregate, so the church broadcast the services over Facebook and YouTube. 

"Although the original 2008 system had a battery backup for uninterrupted power, this was never used and when thused,ttery failed it was difailed,d.

"The nave is often open to the public when the sound system is not needed, the contneeded, soould be protected from curious fingers. "

These are randomly scattered through the once-readable text, so are hard to find.

How can I avoid this problem? Why must I?

[Re-Titled by Moderator]

Original Title: Proofreading introduces errors