Hi @sasasasaaa ,
In general, if a plugin follows WordPress coding standards it should work fine with Hummingbird too.
Is it possible to get the forms loaded on cached pages?
It should work out of the box, there shouldn’t be any interference with Page Cache to cause forms to not load.
Is the cached page sent to the user before most of WordPress was loaded = the plugins aren’t loaded yet?
I’m afraid, I’m still not sure whether I fully understand what exact issue you are facing. Hummingbird uses Page Cache and it would cache the page and its content at the time when a user visits the page. So the cached page what a user seems once all the required content is loaded on a page.
If you are facing any specific issue then please do let us know further about it so that we could check further if needed.
Kind Regards,
Nithin