Hello,
Our default child theme does not have the code you mentioned, only this is there – https://prnt.sc/FQl1V-Zu3WL8
We are not responsible for custom code in your child theme.
Our Remove Query Strings From Theme Static Resources option works fine. URL of video you can find in the Private Content area.
This error – https://prnt.sc/hA6doFTJK-3u is caused by code in your child theme https://prnt.sc/JwwxsCsw4Ybs (if it is commented, there will be no problem)
The disappearance of content is possible due to the cache plugin, namely due to the cache not being renewed, not all cache plugins do this automatically (mainly after switching themes) and it is advisable to clean it manually https://prnt.sc/gzSLTQLqdTk8
Regards