/clear command next to comparator only output signal if it clears more than once

What are you trying to achieve. If you have the items in your inventory it will activate. The setblock clock is so fast, it clears before the comparator has time to turn on because it turns back off again when the player has no items.

and that is the problem, I thought the fact the comparator doesn't have time to turn on was a bug. I don't really know, but the comparator should turn on, even for one redstone tick, that would be more handy 🙂

The setblock clock is so fast it turns off and on a few time inside 1 tick. You'll have to use a comparator clock or something slower