I doubt this is anything to do with SOLR. Alfresco seems to be complaining about the storage used value not being set and being mandatory on the users account (note the description Type: Person, Property: sizeCurrent). This will be held in the database somewhere, not SOLR. You can set quota's for peoples account and it looks as if the value for "storage used" is not set and for whatever reason Alfresco requiring it to be set. This could be a difference in defaults or settings during the upgrade.
Fixing this is likely to be tricky because I suspect you will have to update something in the database directly which is always a risk.
I do not know if you are using quotas on user accounts or not, but you might try switching it off in alfresco-global.properties and on each user account and see if that helps.