Hello Sultan, just want to say that I am so happy with your ROM! Such a massive improvement over OxygenOS, happy I switched, should have done that ages ago. Thanks again!
That could be because of a corrupted download.
Download it again http://techerrata.com/file/twrp2/bacon/openrecovery-twrp-126.96.36.199-bacon.img and flash it again.
If your recovery partition is itself corrupted, you can't use it to flash anything...