As explained the issue has nothing to do with Ad Inserter.
Please read my explanation above.
Why do you believe it is Ad Inserter problem?
It only inserts your codes according to the settings.
The theme providers have also faulted the plugin.
What makes them think so?
From the theme providers I would expect a detailed explanation of what exactly is wrong.
When the entire Ad Inserter plugin is disabled here, the page works well.
This doesn’t prove anything. When you disable the plugin you actually disable insertion of blocks – your ad codes that break the layout.
Have you tried to disable insertion of the blocks instead of disabling the plugin?
https://adinserter.pro/documentation/debugging#back-end
Have you tried to change the theme? The best test is with default WordPress themes like Twenty Nineteen or Twenty Twenty.
Are the isses still present?
A different website using the same theme I am using has inserted Adsense code in this page and it’s working correctly.
It is not enough to use the same theme. You should also use the same plugins configured the same way in order to compare this way. Otherwise the sites may not behave the same.
Please post links to both sites (with remote debugging enabled) so we can compare.