Hi Hanna,
We provide XenForo services from web hosting to regular maintenance and set up. I've sent you a private message.
Please check my signature for reviews.
It seems you have gone through the hell, I can feel how frustrated it can be.
We (Todo10) are a small company which provide tailored web services including web hosting. For example we've been hosting Vi-Control.net since 2017 and @creativeforge can let you know about the difficulties we've gone...
Of course. We've done several imports from vBulletin Cloud including redirects in the case from vBulletin to XenForo so URLs won't be broken after the migration.
We can help you for sure, we have migrated forums with more than 13 million posts and lot of attachments as well.
It's also very important to keep in mind redirects and verify SEO on page after the migration because traffic can decline after then but things are done in the right way it won't...
The Image Optimizer addon of @truonglv is causing issues with missing attachments, maybe it's related:
https://xenforo.com/community/threads/image-optimizer-for-xf-2-0-paid.140261/post-1663730