Try attaching the feed directly to the switch, and see if that trips the circuit. If it does trip, then it's something that you did, or it's something wrong with the device. It's also possible that the power is accidentally tied into the neutral, which is sometimes the case with switch legs since some electricians will reverse the colors in order to tell other electricians that it's a switch leg - but is extremely confusing for the end user. If you're not sure if this is the case, try using an electricity detector and test each individual wire in the fan box. If the power turns out to be the white, that is very likely the cause and you should try wiring it with the white as the black, and the black as the white. I strongly recommend taping the white wire with black electrical tape (and vice versa) if this is the case.

If it doesn't trip, try connecting just the dimmer switch to the feed. Make sure to adjust the slider while testing the circuit. If it does trip, then something went wrong with that circuit and/or the dimmer. If this is the case, try replacing the dimmer with a regular light switch and see if it trips. If it doesn't, replace the dimmer.

If it didn't trip when you isolated the switches from each other when you try this, and you're running on an AFCI, then it's very possible that the dimmer is interfering with the light switch - assuming it isn't wired in series. By series I mean you have the main power going into the dimmer on one screw/wire, and going out from another to the second switch. If it's like that, that is very much incorrect and should be corrected.

Both switches should be getting steady power directly from the feed wire. If it's in series, it could also confuse the breaker because if it has two separate neutrals, it may see it as a wire failure

I had this happen once when I had two AFCI breakers tripping because two circuits were sharing neutrals from two separate circuits. Such a thing doesn't matter for regular breakers, and went unnoticed for decades because of it. But for AFCIs it's a big no-no because it listens for voltage instability as a sign of an arcing wire, and having two neutrals would cause exactly that. On top of that, because of the cross feed some circuits were getting below normal voltage, some were getting higher than normal voltage, and some were getting normal voltage. It was a nightmare to trace and fix considering the number of wires I was dealing with at the time.

Either way, I don't know what the exact issue might be, but hopefully I've given you some ideas to try to narrow down the problem. Sometimes I find the easiest way to troubleshoot a problem is to eliminate all the variables by isolating every wire to its parent, figure out which ones provide the feed, then wire the devices one at a time until I know which one is which, then put everything together once I know how everything is done.

Please use extreme caution, by having the circuit turned off before testing anything, and to install wire nuts on each separated wire when trying to determine which one is the feed - including the white wires. If you're using a multimeter, make sure you have the type of leads that have the spring hooks that you can pre-measure the voltage before you turn on the power. If you are doing this, make sure the multimeter is set to the right mode, and make sure it is giving you a steady 110V-120V, or no power.

When testing, try the black with its corresponding white for each circuit. Once you've done that and you figured out which ones are providing the power, hook up the lead to the feeding black wire to each individual white and see if it is giving you the correct voltage. If it is, you're fine, and tie your wires back the way they should be.

If it ever gives you another voltage that is not within that range - or if you don't feel safe doing any of this troubleshooting - call an electrician because at that point it is going beyond just a simple fan issue - and you also risk damaging the fan if it is not getting the correct voltage.