Output in Responsive HTML takes forever when indexing attachments.

In addition to what Peter said, have you tried using different attachments in your single attachment test, to confirm it isn't some quirk of the specific attachment (I'm not sure what attachments your using or if they are all the same type for example).

Your subscription entitles you to upgrade to the current version which is 2022.3. I'm wondering if that is worth trying. You don't have to uninstall 2019 as you can have both versions running.

If you don't want to go that route, I'm not sure what to suggest. You know what is causing the lag but how to get past it.

When you say "more than one", do you mean that literally and that two cause the problem?

I think I would create a new preset and see if that changes anything. Also try with a frameless output to see if that makes any difference. 

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