It seems your issue is caused by dirt/debris between the chain and the guide bar rail.
Clean the guide bar groove from the sprocket tip to the rear of the guide bar. Use a sharp object (e.g. pressurized airbrush, thin wooden stick, 2 mm screwdriver) when removing dirt.
Note: It is recommended to change the side of the guide bar every now and then.
1.
Remove the side cover / clutch cover and take off the chain from the guide bar.
2.
Make sure that the rivets on the chain are clean and free from debris that could prevent the chain to fit well in the guide bar rail.
Note: Video only available in English.
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3.
Clean the guide bar rail
4.
Reinstall the chain correctly onto the rear sprocket and guidebar.
<video width="100%" controls><source src="https://mavenoidfiles.com/products/9486457/255339f87da02291/Refit_the_chain.mp4" type="video/mp4"></video>