The key to successful inmast furling management is to understand the mechanism and operate it accordingly.
Until I did, I had a few jambs - very frustrating.
Jambs are invariably caused by the sail initially being furled, or unfurled, with insufficient tension -so that some turns of the sail around the central rod can bunch up and jamb in the mast slot.
When retracting or deploying the main, it is important to maintain some tension on the sail to ensure the turns of the sail around the central rod are firm.
Viewed from the top of the mast, the sail is wound in a clockwise direction around the central rod. So, when viewed from the stern, the sail enters/exits the mast from the starboard side of the mast slot.
With the wind on the port side, the sail will tend to bind on the starboard side of the mast slot. Depending on wind strength and amount of exposed sail area, this added friction can make furling/unfurling very difficult or even impossible.
Conversely, with the wind on the starboard side, the sail will be clear of the sides of the mast slot and the wind will assist the unfurling of the sail. If you're not careful, this can lead to an uncontrolled, unwanted unfurling of the sail.
Exploiting these effects can make handling inmast furling safer and easier.
To furl with nice tight turns on the mast rod, get some starboard side wind on the sail and furl it whilst maintaining tension on the outhaul line.
Unfurl with some wind on starboard side and always maintain some tension on the furling line whilst operating the outhaul.
Inmast furling, when used correctly, is great for singlehanders like me.

regards to all
allan