The following concepts (models) may be considered unsettled, even if the Physics community has adopted the concept as part of its standard model (generally accepted as the standard explanation).
Commonly accepted (Standard Model) Physics concepts may be considered unsettled if supporting experimental evidence is unclear or is itself unsettled, and competing minority explanations may tend to lead to less complex or less paradoxical physics models, and if competing explanations are compatible with existing experimental evidence and observations.
For example, the standard model of physics adopted the "Copenhagen Interpretation of Quantum Mechanics", or in-deterministic (random) model of quantum physics. The standard model interpretation of quantum physics was rejected by Albert Einstein in favor of a model he called "Hidden Variables" or deterministic (non-random) quantum physics. A minority of physics today believe that science will eventually prove that Albert Einstein's deterministic (non-random) model of quantum physics is actually the correct model. [1] If this minority of physics is correct, then quantum physics may be understood using Albert Einstein simple and elegant deterministic (non-random) model, free of the bizarre paradoxes associated with the current standard model of in-deterministic (random) quantum physics. For example, entangled particles would be understood simply as identical copies of particles that do not communicate instantly over infinite distances (see analogy Coin Flip and Copy Machine).
[1] NewScientist Magazine (Mark Buchanan), 3/22/2028, Quantum randomness may not be random, NewScientist Magazine, 3/22/2008 issue 2648, (see Quantum Randomness)