I have the fret started and have switched hands, pulling from the end and heating from the middle, working very slowly. The long white flakes at the edges of the fret slots and along this fret are remnants of previous glue.
Now that all the frets are out, I can see which of those old chips are really loose. Notice the "blister" in the fingerboard just below the lower square inlay. This one is typical, unfortunately.
By the way, here's what the frets look like. One is clean and untouched with the overhang still intact. The other (like about half of them) has been cut short and nicked heavily on the bottom edge to make it fit more tightly in the slot.
This next bit is difficult to show. In order to reglue the chips, I'll have to work on one at a time. I'll run some thin Cyanoacrylate (superglue) under a loose chip, and spray some catalyst (accelerator) on the blade of my flexible putty knife. Before the catalyst dries, I'll immediately mash the chip down on the fingerboard "ironing" it in place by pressing hard, moving the knife slightly so that it won't become stuck. This little trick works quickly and surely.
I'll fill open gaps with medium-viscosity cyanoacrylate mixed to a paste with lampblack:
On this guitar there's no hurry so I won't use catalyst. If I were to use the catalyst I'd dab a little into the hole and allow it to dry before adding the paste. That way I'd reduce the chances that it might turn white as it hardens.