FLR (HRO) More documents required

Dear Friends!!!

I need a little bit of advise and i am bit confused why immigration has asked me "Medical reports" of me from GP.
History:
Tier 4 Student Visa 2012 (came in UK Feb 2012)
Visa revoked (2014) college sacked me due to poor attendance
Relationship with British partner started April 2015
Application Submitted on Flr Hro: July 2018
Application fee paid
IHS paid

Flr Hro Application based on relationship for over two years, got 2 years old biological son and 11 years old step son. Partner is English British.

But recently received an email from HOME OFFICE asking:

Thank you for your application for leave to remain in the UK.

In order to further consider your application, please can you provide us with;
A copy of your up-to-date medical records.
Our aim is to make a decision on your case promptly. To enable us to do this please send the requested information to PO Box 3468, Sheffield, S3 8WA by 7 March 2019.

COULD ANYONE TELL ME WHAT DOES THAT MEAN? ARE THEY GONNA ISSUE ME VISA? HOW LONG DO THEY NORMALLY TAKE TO RESPOND AFTER SENDING ADDITIONAL DOCUMENTS? HAVE I GOT ANY CHANCES OF APPROVAL? ANY SIMILAR CASES ANYONE KNOW?

THANK YOU