When a stream of water flows over a hopper, if any XP orbs flow through that hopper they get caught and never make it to the end of the stream. This is an issue as the XP in my monster farm gets to the player via the water stream and the items get collected in a hopper but the XP orbs don't get collected by the player.
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GoldenHelmet
I don't see any xp orbs in your screenshot, so it is difficult to assess exactly what the problem is. However, I think you are likely experiencing MCPE-120829: xp orbs appear to stop at flowing water, but this is a visual desync from their actual position.