this happened to me more times than I can count, I don't kniow why that happens, let's hope someone does and shares the solution
What I always do is:
Flash this via fastboot, you can flash just the IMGs one at a time (except recovery)
1 fastoot pyxis_global_images_V11.3.3.0.PFCMIXM_20191101.0000.00_9.0_global
Flash this via TWRP
2 xiaomi.eu_multi_MI9LiteMICC9_9.10.31_v11-9
Then flash this via fastboot flash system
3 PixelExperience_ARM64AB-10.0-20191208-1826-UNOFFICIAL
after flashing everything, do a "fastboot -w", always do that, helps avoiding bootloops
you can also try this somewhere in there
./fastboot --disable-verity --disable-verification flash vbmeta (vbmeta.img file)