Start by turning off your tablet, and remove USB cable if connected.
Or are you in a boot loop?
Do you have the stock ROM downloaded?
Download QTPS if you haven't already.
Move your extracted ROM files into the "bin" folder where QTPS was installed.
Run QFIL from that folder, it installs with QTPS. Version 126.96.36.199 of QFIL worked for me yesterday.
Also make sure you try different USB cables, here it can actually make a difference, also try USB 2.0 port.
Have you configured QFIL to use "ufs" device type?
All you should need to change in QFIL config is device type and that it should reset after download.
Select "flat build", load firehose_ddr.elf as programmer.
Press Load XML in Qfil.
Select ALL of the rawprogram files. Hit OK.
Next, select ALL of the patch files.
Now connect your tablet.
Press VolUp + Power button at the same time until you hear the PC recognizing the tablet as a Qualcomm device.
You should now be in EDL mode, tablet screen should be off.
In QFIL, select the correct port, Qualcomm 9008, if not already recognized.
Then press Download.
It is important you've set up QFIL before you are ready to flash the tablet, since it only stays in flashable EDL-mode for a short while.