Widevine L3 to L1

Hello everyone.

Yesterday accidently i had my sensors on OnePlus 7 pro deleted on a custom rom.

So i was forced to flash the persist.img file on my device to get those sensors working.

The sensors were working back to normal then.

Now as the custom rom had some issues, i flashed back the stock firmware.

I am now on stock OOS firmware 9.5.3 GM21AA on my device.

Problem now is i am unable to stream in HD on Netflix & Amazon prime video.

The security level to my surprise is L3, instead of L1. To get this back to L1, i have done the following things:-

1) Locked the bootloader after flashing the stock firmware.

2) Formatted & installed the latest oos 10.3.2 GM21AA on my device.

3) Used MSM tool once to recover the stock firmware on my device, now my device is on oos 9.5.3 GM21AA

After trying all the above troubleshooting steps, i got no luck to have my widevine back from L3 to L1.

Is there any possible workaround for this issue?

Can anyone help me in this or have i lost my L1 forever?

Is the only way to fix it, is to take my device to the service centre?

Any help would be deeply appreciated.

Thanks.