The stock Frog front steering is known to be flawed, so easy to fall off. It may be better of to replace the entire steering block with one from the TT02B. With these, you can use the TT02B steering knuckle directly on the Frog.
Download: upgradeparts-frog-frontchub-convert-tt02b v1
Note that if it appears very large in your slicer, resize it to a scale of 1/10.