Whirlpool AWE 4519P - "Clean filter" appears in the washing machine

I have a Whirlpool AWE 4519P washing machine, during washing, when rinsing, the message appears - clean the filter, I cleaned it once, at the bottom of the washing machine, during the second wash - again, when rinsing, the message appears - clean the filter, again. I cleaned, I note that during 1 cleaning I did not find anything, no coins, buttons or dirt, the washing machine is 18 months old, about 1-2 washes a week.

At the 3rd wash - the information appears again - clean the filter, will it be like that every time, I don't know what's going on, if I can do something, it's been 18 months since the purchase and I can't find a receipt - I only have a pro forma invoice for order.
Help me, I'm alone, so I don't know if I should unscrew anything, look somewhere but where and how.

A possible cause of this error could be a clogged hose connecting the washer tank to the drain pump.

A colleague tells me well, and in the meantime a small sock or a napkin has not been lost?
The first is - check the drainage hose - the corrugated one, remove the end from the siphon [check the siphon itself if it is not blocked, if the siphon is ok then] unscrew the filter and blow hard into the corrugated pipe, maybe some scale will blow through the filter, muck etc.
If this is useless - after cleaning, perform e.g. a wash cycle - unfortunately, to check the rubber hose> tank-pump, note - in this tube, under the tank itself, there is a valve ball Unfortunately, this operation requires partial disassembly of the washing machine.
If it did not help - pump to be replaced - damaged rotor clutch.

Thank you for your answer, I already have a point of attachment and what to check, and as for the loss of a sock, I don't remember, I checked if something had fallen between the drum and the chamber wall, but there was nothing. after 3 pieces of information - clean the filter - the water from the filter cover drained, I cleaned the filter, the chamber, the pump impeller checked, and the washing was finished, but this information will appear again - clean the filter, but I know what to check next, thanks

And what about the drain hose, because it's not written? And how did you check the pump impeller clutch - it is practically a non-dismountable element?

I'm sorry for writing back now, but it's time for holidays, trips ...
indeed, first I checked the hose and of course the siphon, and it turned out that the siphon was clogged with dirt, washing residues, it was cleaned, the laundry was empty and it worked without information about cleaning the filter. so thank you for the advice, advice, I applied it, it worked.
I end the thread as a success