Deed of variation leasehold property

ARBI

Hello

I hope to get some help, as I have sold my 2 bed flat and I was due for completion but the buyers solicitors requested a deed of variation over a paragraph clause on the lease.my solicitor believe that the paragraph is a general clause and the lease does not require amendment. I am also in the same thought.

The lease say
If any lessee assigned or transferee of this lease fails to give notice to the Secretary of the company for the time being of their intended registration within 2 months of any assignment or transfer of this lease there term hereby created shall thereupon absolutely determine but without prejudice to any claim by either party against the other for any antecedent breach of any of the covenants herein contained.

If I understand right the paragraph requires the registry transfer within two months.
I would like to know why the buyers solicitors wants this removed, I understand it's a harsh clause but surely everyone will transfer asap when they buy?
I have filed for a deed of variation of £252 upon waiting an answer from the freehold.i am worried they may

1. Say no to this paragraph removal
2. Take it off but it will come at a cost or even requires the amendment of all leases.

I understand the buyers solicitor and covering their back but surely I bought 7 years ago and this has not caused a problem.
Has anyone had a similar issue with their lease? my lease term description of the property covenants seem ok but the buyer solicitors want it removed. They do not want to even complete and get the new buyer to amend it at their own time.