These are the steps you need to consider when upgrading:
If you’ve already updated all your modules properly, then install this module and enable it and check if it finds any deprecated modules that could be causing issues for you: https://forge-vtt.com/bazaar#package=deprecated-modules
I think if you follow these, you’ll get your things sorted.
There will probably be modules you can’t use with 0.8.6 and sadly that might just remain that way if people have abandoned them.