Hedge trimmer lower blade is getting of the eccentric block

Hello,

have the Poulan Pro PP6000H hedge trimmer attachment for some time.

Lately I noticed it is not cutting as it used to cut.

checking it I found that the blades are not timed and so from time to time almost move together instead of opposite directions.

I opened the unit and found out that the lower blade is getting off the eccentric block. I tried several times to put it back, assembled it but still after running for a minute or two correctly, it happened again.

Any idea on how to fix it?

thanks in advance.