Delay in H4 visa Extension for 8 months even after USCIS considering old biometrics

Hi,

Filed I539 - Application to extend status on 04/13/2020
Received letter from USCIS that it is not necessary to appear for biometrics on 05/21/2020
Escalated the delay in time to issue visa on USCIS website on 11/02/2020
Received letter from USCIS stating that based on fluctuations and variables that impact the processing, the VSC allows 30 days beyond the posted date before the case is considered “Outside of Normal Processing Time” (ONPT) on11/13/2020

No idea why there is so much of delay in granting visa though USCIS is considering the old biometrics data.

yeah, this is the sad part of the delays.
There are no guidelines for them to adjudicate. There are many delays with processing.
There are some still in similar situation as yours, so you are not alone.
You can track the changes in processing times at below link