Is it crystallized? You can tell if you use a hive tool to lift the cap from one or two cells, then push a cocktail stick into the honey. If it comes out with granular stuff on the stick, it is crystallized.
The other problem could be jellybush (manuka-type) honey, which is thixotropic.
For either problem, the first thing I would try is something that I think @KieranPI suggested - repeatedly open and close the frames 5 or 6 times. Try to do it around midday, when the honey will be warm as this helps the flow. Then leave it for several hours.
If it isn’t jellybush, but it is crystallized, personally I would try a sous vide melt method. I have never tried it, but I have all of the equipment and it should work.