We’re aware of this issue which happens in the update thread due to PHP opcache storing the old version of an updated ACF Class.
Unfortunately, there’s no way to resolve this other than performing a one-off manual update to get past the update. While the error will still happen for you in the update thread, it is only present for the update and no end user will ever see the error. You’re free to ignore it and everything will work find on the next page load.
SPM detects the PHP error triggered in the update thread and performs a rollback for protection.
