Tunze Osmolator 3152 only works immediately after plugging in

Hello all,

I recently got back into the aquarium hobby after about 4 years. I set up my IM Lagoon 25 on 5/28 and am finishing up my cycle currently.

I had a smart micro ATO on my old setup that worked perfectly but unfortunately must have been stored with some moisture because one of the plugs was corroded when I pulled it back out and it didn't work any more when I went to put it on my tank. I went to my LFS and purchased a new Tunze Osmolator 3152 which seemed to have worked well for the first 10 days but over the last 4 days it has not been topping off my tank at all.

The pump works when I unplug the power adapter and plug it back in. The pump will run until it forces the float up but it won't re-engage at all after that initial top off. For example, I set the float sensor just above the current water line and I unplug the pump and plug it back in and the pump will go for 5-10 seconds or however long it needs to so that the float rises (nowhere near the 1.8 minutes that would trigger the safety mechanism to stop the pump). At that point in time, the pump will not engage again unless I unplug it and plug it back in. I have two media caddies in the back filtration chamber that if I pull them up and out of the tank, the water level drops enough to lower the float all the way down, yet the pump does not engage. I can physically lift the float sensor out of the tank and shake it up and down and the float moves freely but no water is pumped from my ato reservoir.

I never had any issues with the optical sensor on my old smart micro ato but this float mechanism seems less reliable based on my limited experience. I have tried it both with and without a piece of cardboard separating the magnets further to avoid interfering with the float but that doesn't seem to change anything.

If anyone has suggestions I would appreciate hearing them! I may end up just eating the cost of the Tunze ato and buying the newest model of the smart micro ato and trying that. Unfortunately my only option at my LFS is to return it for a replacement (because it was opened and touched water) and at the current moment, I don't think I want an ato that relies on a float.
 
Just to add more information:

This morning I checked the tank and saw that it had not been topped off overnight at all. I unplugged the pump and plugged it back in and I counted 32 seconds that it ran continuously to raise the float sensor back to the desired water level. After it had finished, I removed one of the media caddies to lower the filtration chamber water level and drop the float. The pump did not and will not kick back on now unless I unplug it again and plug it back in.

I will not be surprised if this is some user error but I can't for the life of me figure out what is going on. As I mentioned in my original post, this ATO worked with no issues for over a week before it started doing what it is doing now.
 
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