All recipients of ESA must have their claims periodically reassessed unless all four of the following criteria are met:
1. the level of function will always meet LCWRA (limited capability for work and work-related activity) criteria;
2. the condition will always be present ;
3. no realistic prospect of recovery of function ;
4. unambiguous condition.
The guidance given to staff as to the types of conditions which might meets all four such criteria includes the following list:
• Motor Neurone Disease ;
• severe and progressive forms of MS, Parkinson’s;
• all dementias;
• Huntington’s;
• severe irreversible cardiorespiratory failure; and
• severe acquired brain injury
For all other conditions the person carrying out the initial assessment (and each subsequent assessment) is required to tick one of the following six boxes:
"I advise that work could be considered within:
• three months
• six months
• 12 months
• 18 months"
"I advise that work is unlikely:
• Within two years
• In the longer-term"
So it seems that the assessor in your case ticked one of the boxes higher up the list, requiring your condition to be reassessed at this stage.
[My answer is based upon reading a House of Commons briefing paper, which I've uploaded for you here:
http://www.upl.co/uploads/CBP78201543085244.pdf
together with the training document for assessors, which is available online here:
https://www.scribd.com/document/360863511/DWP-WCA-Guidance-on-Severe-Conditions ]