Inconsistencies between 1rm and other rep maxes

I've noticed that my one rep max and my other rep maxes are out of whack according to just about every calculator I can find.

I can always do far more reps at slightly lower weights; or, alternatively, I cannot do quite as high of a 1rm as my lower weight sets suggest.

For example: I hit 205x10 on bench and had some left in the tank. Exrx gives me a 273 1rm; symmetrical strength gives me a 276 1rm. I have never done more than 240.

Another example: I can hit 275x5 on squat, which suggests a 309 squat, but I stalled at 290 this week.

Do you think it's just (1) fatigue or (2) form breakdown or (3) fear or (4) something else?

I've been doing a slightly modified nSuns LP since January. I'm 5'8'' 155lbs and my heaviest lifts this last cycle were:

sq 290x1 (hit 275x3 right after, tough but had another one in me for sure) be 220x4 de 365x1 (I am focusing on RDLs and hamstring work and limiting my DL maxes right now) ohp 145x5