Light travels at a constant speed in a vacuum, but changes when subjected to forces such as gravity. We use light to report on many situations outside Earth. This means our knowledge is limited by the nature of light.
Why focus only on Photons and our inability to determine their mass? After all, light not only acts as a wave, but also as a particle. A particle has mass. This has been confirmed that light does bend when passing the sun.
So, there may be characteristics of light that we do not understand. Start with what we do know. Get rid of fuzzy terms that really do not help us understand.
Light has characteristics of both a wave and a particle. The wave part is easier to investigate. The particle part changes into energy when it is stopped. Different wave lengths have different energy, but bends the same amount when affected by gravity.