Odd permissions issues under Mojave (10.14.5) after Migration

Transferred a set of files from a Macbook pro to another via Migration Assistant. I now have an application (.app directory) in /Applications that cannot be changed (chown, chmod, rmdir, etc). It is owned by a non-existent user (id 502) which didn't transfer across. I tried to create temp user with this uid without success.

I have tried:

- number of UNIX commands as root (directly and via sudo)

- setting SIP to disabled (csrutil disable in Recovery Mode)

- Boot in Safe mode (SHIFT key on startup and confirmed through System Report)

- Both of the above

- Running First Aid in Recovery Mode on APFS container and volume

• I have checked for extension attributes (@) and extended acls (+)

In all cases I get "Operation Not Permitted" error. Most online help suggests that this might be SIP related (which can't be case in above scenarios as it is disabled).

What am I missing? Trying to avoid restarting the whole migration process again.