I am playing on a modpack which includes TFC and AE2, and we have some issues with some items (particularly ingots and a few other items) not stacking when autocrafting them. (The autocrafted items don't stack with the non autocrafted ones).

The cause seems to be that the non autocrafted items have the NBT tag

{"tfc:item_heat": {heat: 0.0f, ticks: 0L }}

while the autocrafted items (with gregtech machines) do not get this tag.

as confirmed by using the /data get entity @s SelectedItem command:

Feels to me like this tag should be removed from items which are not hot?

Minecraft version is 1.20.1. Terrafirmacraft version is 3.2.7

The autocrafted items should have this tag, I do not know what gregtech is doing that is preventing them from instantiating and having capabilities. To be clear:

• This tag is not part of the stack tag, this is part of the capability data (which gets managed by Forge, and saved to the stack tag in certain cases such as serialization)
• This tag is indicating that there's a heat capability attached to the item which is attached by TFC on AttachCapabilitiesEvent, and should be present on every item stack that can be heated.
• The problematic stack is the one that does not have this capability information, not the one that does.

In the tfc client config, enableDebug can be used to show the capability NBT separately from the stack NBT. Without any further information this seems like gregtech doing something wrong to create these stacks without a capability.

Without any further information this isn't solvable on our end, we're doing everything correctly as it seems. See also the linked issue