I think you should contact the UK CAA Medical Deptment and see what their view of the SOLI process is. Either they can progress what the LBA want or they can't, the latter would seem to apply. As the process has not completed you now have a UK Part FCL Licence which you should revalidate or renew in the usual way, that will require a UK licensed examiner.
It might prove easier to do a 3rd party licence conversion to Germany, that way you retain your UK licence and get a German EASA licence on conversion.