as long as i stay in the first chunk the command return a bastion 600+ blocks away
when I move to the next chunk, in the direction of the real closest bastion, it returns the correct one, at 140 blocks away
Seed: -953628641355065

Edit:
at X=432 and Z=-1 in the nether the command fails to locate the fortress next to the player and returns one at 390 block aways