3.3V / 1A boost converter TPS61025 drops to 330mV when loaded with 5.5 Ohm - why?
Circuit looks OK. I am going to guess that you have not soldered the ground slug (datasheet calls it "PowerPad") at the bottom of the IC to GND at all. Besides the thermal connection, the IC may be relying on a low impedance electrical ground on this ground slug.

Best would be to redo the IC soldering and use a hot air reflow station to get the ground slug soldered down to the GND plane.

An alternate hack would be to remove the IC, scrape off the soldermask so you get exposed GND plane copper next to the IC all the way to the slug area, cleaning the board and putting flux on the board and IC bottom, and then use a really huge tip on a soldering iron to reflow the solder so it creeps underneath to the IC's ground slug. You will need a huge tip and the iron temp cranked up to heat up the ground plane. You need good heat, a clean board with flux to help wick the solder under there.