Broken Links + User login issue + Error when viewing certain orders after moving OC 3.0.2.0 to new server

I've recently moved OC 3.0.2 website to a new server. I've made all the necessary changes and the website is working well with a few glitches below:

1. When clicking on viewing orders, i receive an error 500 when viewing certain old and new orders.
2. Many broken links when viewing certain pages. How can i fix these?
3. When a user is on the checkout page, when clicking login and after entering credentials, nothing changes. No information is prepopulated in the address fields and it doesn't show that the user has logged in. Header still shows the "login" link.
4. The bootstrap.css file keeps disappearing in admin/view/stylesheet/ causing the admin panel layout to change. how can i set this not to disappear or is it possible that someone is accessing the directory and deleting this?

All suggestions would be helpful as I've checked the error.log file which is currently empty, even though the feature is enabled in the admin panel.

Those are very specific questions that have no straightforward answer. If you'd like commercial assistant you can send me a PM