Help Identify siphon break cause

[Schulks]

I walked in the room and my aquarium siphon is completely broke. I've been home all day and just walked out of the room for 10 minutes. I haven't adjusted the gate valve or pump speed in many months.
The sump water level is way up from it.

I'm going to start readjusting the gate valve but how can I try to understand what just changed?

Did some algae just pop out of my gate valve that has been there for 5 months?

 

[DCR]

I would suspect something changed with your pump/return to reduce the flow and increase the level in the sump. The water drained down from the tank. DC pump controllers have been known to malfunction in this way.

 

[Schulks]

I would suspect something changed with your pump/return to reduce the flow and increase the level in the sump. The water drained down from the tank. DC pump controllers have been known to malfunction in this way.

I fairly certain the pump is running at the same wattage as normal. I think this means it is not slowed down.

 

[Schulks]

Do others people's systems do this?

 

[Gribbles]

Snail blocking your overflow?