Second delay email

Hi, I got another delay email yesterday (Jan 26) after receiving an initial one on Jan 9th and am wondering if anyone could provide some insight. Here is some additional information:

Biometrics: 28/11 (Priority)
ECO: 2/12
RFE + docs submitted: 8/12
Delay email: 9/1
2nd delay email: 26/1

Here is the email I received yesterday - it is slightly different from the first one I received (which was the typical one):

"We continue to be unable to make a decision on your application.  For up-to-date information on processing times, visit <...>

Your application is subject to additional enquiries and enrichment.

Do not contact UK Visa and Immigration, we will contact you if we require more information.

Please be assured that we will continue to seek to progress your application to make a decision as soon as possible.

A visa application may take longer to process, if for example:

* the information in the application is not accurate or requires further consideration
* Applicant needs to provide further evidence, for example evidence of funds
* supporting documents need to be verified
* attendance at an interview is required
* further information is required on the personal circumstances (for example if someone has a criminal conviction)
* UKVI is experiencing increased visa demand

yours

UK Visa and Immigration"

I haven't heard anything else, no requests for further documents, etc.
I am a bit confused about the "Your application is subject to additional enquiries and enrichment." part as I do not believe I have seen this before with other applicants. Our RFE was proof of employment as we stupidly forgot to include the employer letter. My partner also got promoted and a pay raise last August. I wonder if that has anything to do with it?

Has anyone seen/heard of this before? I thought our application would be straightforward as we tick all the boxes (but obviously forgot to submit some evidence initially).