It's a Shimano RD-AL11, lower spec than M700.
https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=Shimano+RD-AL11&_sacat=0&LH_TitleDesc=0&rt=nc&LH_PrefLoc=2
https://www.disraeligears.co.uk/site/shimano_al_11_al11_exploded_view_-_562b_march_1984.html
Select which gear is suspect, apply the brake, & apply force to the crank whilst watching for the chain riding up the teeth on the sprocket. If it rides up it's replacement time.