This is a known issue I probably should have made a note about, but I figured most people wouldn’t actually update Bedrock since it’s an uncommon situation.
To fix it, you need to do the following:
Delete vendor/ and wp/ dir
Delete composer.lock
Run composer install again
Since your vendor/ dir is managed by Composer, it shouldn’t do any damage to delete it. And just a note that deleting composer.lock and letting it re-generate could potentially update some versions of packages depending on how you defined them.
edit: Actually you may only need to delete your composer.lock file now that I think about it. Or maybe wp/ as well like you did. vendor/ shouldn’t even matter.