welcome to LL, Lisa and Jack!
Will you be able to get some spot checks today? It looks like Jack is already clearing his bounce. Since the 268 is quite a bit lower than the HI last night, you'll want to get a spot check fairly early today (maybe +2, if that hasn't already passed) to see if he is still dropping that fast.
It looks like Jack is doing well. You're definitely on the right track. The 38 earned Jack a reduction to 0.75, and it also made him bounce high to the 500s. As you saw this morning, those highs usually clear out on their own. Reducing was the right thing to do, but the fact that you gave 1u last night while he was bouncing is probably what helped him clear out the high numbers so quickly (lots of cats stay high for days after a lower number, so the fact that he only stayed up there for one cycle is very encouraging).
It looks like you have been having to stall shots often because the numbers were lower than you were comfortable shooting. Hopefully the dose reduction is just what Jack needs to keep him just a little bit higher so you don't see 50s at preshot. You're doing a good job of collecting data, so if he does keep hitting 50s at shot time, we can help you figure out what to do.
Because Jack cleared this bounce so quickly, it might be that you don't need to "shoot through the bounce." If he drops too low or too fast today, then make a mental note the next time he drops low and bounces that you should reduce his dose right away rather than waiting for the bounce to clear. Today's cycle will give us a good idea of whether that is the case.
Good job!