tl;dr: applying healing to a force rod to pass upgrade tier 6 fails because crafting a force rod from scratch doesn't apparently set the NBT data correctly; a workaround is to craft two force rods and then craft them together to get the NBT into a state that will let one apply a single infusion (or to creative spawn one in, apparently). The same "bug" also applies at tier 7, for glowstone.
I note that, possibly relatedly, having a force rod with any force power infused into it, or any other infusion, also similarly appears to block the infusion; the similarly applies to all other items, leading to the somewhat confusing situation of appearing to need to craft a new sword for each sword-applied infusion in order to progress through the tiers. I'm not sure if this is intentional, or if one should be able to apply a second infusion - or upgrade the infusion, or possibly even remove one - to a tool one already has improved from base. The fix may be somewhat more involved, depending on what the aim is, and if this is intentional or not.
Also, one can take a sword, apply a forcecraft enchantment, then using industrial foregoing's enchantment extractor, remove the enchant; this does not appear to restore the NBT to a base state, leaving a non-force-enchanted item that will not accept any other force enchants either. The NBT matching is, apparently, somewhat overly picky. This may, of course, be entirely unrelated.
General Info
Suggestion Description
I see a bugrep on FTB Skies and don't see any mention in open/closed issues here, so figured you might not be aware:
https://github.com/FTBTeam/FTB-Modpack-Issues/issues/4477
tl;dr: applying healing to a force rod to pass upgrade tier 6 fails because crafting a force rod from scratch doesn't apparently set the NBT data correctly; a workaround is to craft two force rods and then craft them together to get the NBT into a state that will let one apply a single infusion (or to creative spawn one in, apparently). The same "bug" also applies at tier 7, for glowstone.
I note that, possibly relatedly, having a force rod with any force power infused into it, or any other infusion, also similarly appears to block the infusion; the similarly applies to all other items, leading to the somewhat confusing situation of appearing to need to craft a new sword for each sword-applied infusion in order to progress through the tiers. I'm not sure if this is intentional, or if one should be able to apply a second infusion - or upgrade the infusion, or possibly even remove one - to a tool one already has improved from base. The fix may be somewhat more involved, depending on what the aim is, and if this is intentional or not.
Also, one can take a sword, apply a forcecraft enchantment, then using industrial foregoing's enchantment extractor, remove the enchant; this does not appear to restore the NBT to a base state, leaving a non-force-enchanted item that will not accept any other force enchants either. The NBT matching is, apparently, somewhat overly picky. This may, of course, be entirely unrelated.