That looks like an adapter designed for rigid plastic conduit.I have used these https://www.screwfix.com/p/tower-male-conduit-adaptors-20mm-black-2-pack/64512 successfully. Using plenty of solvent weld adhesive to seal the conduit into the adaptor to water proof the join.
Are you saying you glue flexible conduit into adapters designed for rigid? I guess that might work from a waterproofing point of view, but i'm not convinced it would be great from a robustness point of view.