I seen this design, but why the permanent magnet ? That would work perfectly with the ordinary shorted cage
At first it does not corrode in the water - except the stainless steel it contains no metal parts at all. The induction rotor needs a combination of at least two metals, what would get dissolved in the salty water environment (the salts comes from the detergents,...). So it allows to place the rotor directly into the wet part.
Seconds it offers larger efficiency, so less losses, so allows to design it way more robust against e.g. stuck rotor (it dopes not overheat)
And the important: With this size the permanent magnet is cheaper than the rather complex induction rotor assembly (just plastic injected into mould with inserted ferrite piece). Because the thing is small, the rag material cost is less significant than the processing and assembly costs.
All the simplification above means way cheaper and in my experience (I've seen this concept in use since 90's) less problematic pump - this time it is the first time I have an issue with such pump. By the way it looks more like there is some manufacturing defect (some flange from plastic molding not trimmed properly,... - as usually, many chances to have something wrong with lousy production) - I tried to look there with a dentist mirror an have seen nothing foreign there.
Anyway, in most of such pumps that i seen, the impeller is screwed on the axis - sometimes with left direction screw thread (opposite to the direction of th3e pump spinning). If you have access to the edge of the axis from the front of the impeller, poke it in place and unscrew the impeller off
The motor usually does not contain any direction guide (no shielded pole,...), just the electromagnet poles are slightly "bended", so the magnet rests angled with no current. Then the rotation direction is random (therefore the symmetrical impeller design). So there is no thread at all. If the impeller is not already part of the single piece rotor plastic is just "snapped" onto the part with the magnet.
And the main problem I have (why I have started this thread in the first place): How to get access to that damn impeller assembly, when there is nothing like any cleaning hole (usually present in the cloth washers) or so...