IRLZ44N MOSFET switch - voltage drop across brushless fan
The gate threshold voltage is NOT the voltage you care about when using the MOSFET as a switch. That is the voltage where the MOSFET just barely starts to turn on.
You want the Vgs required for the rated RDson.
With 3.3V Vgs, you are right in the middle between the gate threshold voltage and the gate threshold voltage given for the highest rated RDson, so it could go either way whether the actual RDSon is a bit higher than rated (works) or a lot higher (doesn't work).
You can figure out what the RDson should be in the conditions you are running at using the Id vs Vds graph to find out what the RDson is at that condition.