Is this rule too harsh?

I have a table rule that if you roll a nat 1 in combat, you roll a D4.

If you roll a 1 again - you accidentally damage yourself, or an ally.

If you roll a 2 - your weapon gets jammed and you are incapacitated until the end of your next turn (unless you have another weapon to use)

If you roll a 3 or a 4 - nothing happens.

I proposed this rule to my players as a way to make nat 1s feel more like a critical failure, with negative effects - just as a critical success gives you double damage.

The chances of rolling a nat 1, and then a 1 or a 2 are 1.25%, which I think is reasonable.

It's always been fine, but today my players rolled 7 nat 1s in 2 hours of playing (ouch). After the game, one of my players said that the D4 rule is unfair and they would never do that to their players. They've not brought this up before, and I think they are just frustrated, but I am fairly new to DM'ing (a year and a half ISH) and I'm always worried I'm not doing well.

Do you guys think it is unfair?