In Legends Canon, it is known that THRAWN can aggravate Force users, in particular Jedi Master Jorus C’boath in The Outbound Flight.
In current canon, Star Wars Rebels Season 3 Episode 21 “Zero Hour” part 2, GRAND ADMIRAL THRAWN “killed” (shot at) the Bendu who gave him a negative portents, which eventually became true.
By Star Wars Rebels show finale, Farewell and Friends, EZRA BRIDGER fought GRAND ADMIRAL THRAWN and space whales left in hyperspace the entire Galactic Empire 7th Fleet.
What happened is in speculative fan-fiction and fans abound begging Lucasfilm to create some kind of full feature length film that details the travels from the ending of THRAWN and EZRA BRIDGER and some other characters, AHSOKA and SABINE WREN and HERA SYNDULLA and her son, JACEN SYNDULLA.
A lost in space and search and rescue show is okay, but dull. Sitting through 2 hours of quest or journey story that seems rather strange in context with the Sequel canon. REY is the last Jedi. Unless there is magic of who her parents are, and if they are EZRA and SABINE like people want, which seems unlikely but cannot be ruled out, REY would have known if one of her parents were a Force user. NOTHING in the Sequels material suggests that 100%. It seems that REY gained the Force spontaneously — a Disney Magic thing to do.
It would seem BAD that REY’s parents would LOSE her and unable to find her anywhere, even on Jakku. EZRA has access to “Between 2 Worlds” — he can go anywhere. SABINE is a MANDALORIAN and kids aren’t just sold off for drinking money without a fight… IJS.
Everyone goes into the UNKNOWN REGIONS near CHISS ASCENDANCY space, everyone will have to RELY on THRAWN to survive. The longer someone spends time with THRAWN, the more he learns about them and learns how to defeat them. He may support, or even act like he supports EZRA and his foibles, but EZRA has taken DARK SIDE OF THE FORCE shortcuts numerous times before and if EZRA were to turn to the DARK SIDE, THRAWN WOULD KILL HIM.
Call it a mercy killing. THRAWN may have “beliefs” to keep the Unknown Regions clean of any SITH or DARK SIDE USERS — call them CHISS ASCENDANCY BELIEFS. It is in their very codex. From the 2012 IGN SWTOR WIKI
While Chiss can work with Dark Side Force Users, they prefer not to work with them due to the emotional instability — Chiss see it as a mental illness and behavioral problem.
THRAWN will see that EZRA goes down that road and he will have to kill him out of mercy. He probably will not lie to AHSOKA or SABINE about what happened, because it would cause THRAWN grief — whatever that looks like in a Chiss, but for some reason AHSOKA and SABINE would understand.