I had no issues at all flashing it for the first time. I used modded/patched Odin3 v3 13.1_3B and G950U1....CRL2 fw. If you're on DRL7 you can flash straight to the unlocked fw. Mine passed without getting any errors. My advice for you is to find the firmwares for the S8+ G955U, NOT G950U.
1.) Download G950U1UES5CRL2 from updato and extract the files. (only for S8 G950U not G955U)
https://updato.com/firmware-archive-select-model?record=F1B6FF120F1611E99F15FA163EE8F90B
2.) Download Patched Odin 3.13.1
3.) Also download the CRL2 to ZSAB file (extract the files and place it intp your SD card)
https://firmware.science/download?url=00000/0000/SS-G950U1UES5CRL2-to-EU5ZSAB-UP
5.) Turn off your device and go into download mode
6.) Plug a USB cable from your phone to your computer/laptop
4.) Open Odin and flash the CRL2 files to your device (remember to use HOME_CSC not CSC.
5.) Once it's complete your phone should restart and be back to Android Oreo.
6.) Turn your device off again and go into recovery mode and apply the ZSAB file from your SD card to update.
7.) Congrats! your phone is on the Android Pie Official Beta
After my Verizon S8 DRL7 was updated to the official beta ZSAB, there was no verizon bootup animation and bloatwares. You get Super Slow Motion, better battery life, and the irritating lockscreen pull down lag is finally gone.