Simply select all of the instances before applying the Bend modifier. You'll then get that thick bar in the modifier stack indicating that modifier encompasses multiple objects, but you can select the Edit Poly modifier below it to alter the single piece. Alternatively, put all the objects in a Group before applying the…
The shape is not easy to see in this picture, but I'd say you could make a flat strip getting that tire-like shape ready and then use bend modifiers to achieve a similar deformation.
Add a STL Check modifier above the Editable Poly base, as well as a Edit Poly modifier above the STL Check -> rightlclick Edit Poly modifier -> "Collapse to". Should fix the problem and is easier than deleting and creating faces ;)
Actually there's a plug for this in Maya: https://lesterbanks.com/2015/05/getting-started-using-the-maya-shell-modifier/ ...and for me as a 'Blenderite', "Shell Modifier" means adding thickness or volume: https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/solidify.html