The biggest problem in current physics that prevents us from moving forward is the reification of concepts as real, physical phenomena: spacetime warpings, wavefunctions and collapses, strings, extra dimensions, parallel worlds, faster-than-light communication...

The story is always the same:

Someone develops a new mathematical tool or conceptual framework to better understand or describe some physical situation.

Then we get used to thinking of it as the real thing.

Then we find that we have to create a new convoluted physical mechanism to explain some quirk of the new formulation (which only happens because we're applying the physical constraints of reality to a conceptual tool that doesn't have to conform to them).

Then we get used to the new trick or concept, so we think it's describing reality again, when in fact we've separated ourselves yet another abstract level from the underlying physical reality of the situation...

Repeat ad nauseam.