Issues when upgrading

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Hello,

I am upgrading a page from v. 8.2.1. to 8.5.1. and I am running in constant issues after upgrade.
For example on a few pages where I have custom made block I am now getting error

"Entity of type 'Concrete\Core\Entity\Attribute\Value\Value\Value' for IDs avID(10849823) was not found" -> allways the same avID (on multiple pages having different custom blocks).

On homepage the position of blocks is getting mixed up, blocks are overlaying each other (not every block), but for example concrete video content block is overlapping Page list block and so on and so on. Cron jobs are also failing due to Foreign key restrains.
I have countless problems and I looking for help or for some one to point me in the right directs to fix this issues since I dont' want to leave the page on an older version of c5.

Thanks to everyone who will take time for me.
Best regards