Los 16 is ending in a bootloop for me too... (also t815) no Chance for me to run that Rom at my device.
Now i am back und Lineage 14.1 with actual security Patch...
If you Are back on Stock, you could Boot into Download Mode and install twrp again.
Important After install twrp in download Mode, you have directly Boot into recovery. Otherwise it is not installed correctly.
Going to Stock via Odin is the way to get your Tablet running again. (thats the way i was going, if nothing helped)
After that, you can install every other Rom you want ;)
In Download Mode you could Re install twrp and Update it to 3.3.1.
Otherwise you could install the Stock Samsung Firmware via Odin in download Mode. That should help to get you tablet running again
That helped to me in the past too. Ok, Going to Stock via Odin. Than reset etc..
But in the end, these Rom LOS16 isnt running in my t815, it just ends in Bootloops.
Now it runs on LOS14.1 again