Hello Vicky - it is always difficult to be precise re such matters until we actually see the application as a whole.
The lack of a plan need not always be significant if everything else is in order and it's clear as to which property/land is included for example
In my experience most buyers, especially those buying with a mortgage, would insist on the seller registering first to hopefully resolve any such issues and to confirm the class of title awarded also. That's especially true with a probate sale as well
I would recommend making the application, request expedition separately and then see where that takes you.
Expedition gets the case to the processing start line but does not guarantee it's registered in the 10 days mentioned - any 'faults' need to be resolved if there are any of course
Request an expedite - GOV.UK