The Ghastlings spawned by the Ghast Trap spell die immediately to 'magic', presumably the lighting strike accompanying them.

Version 1.0, though nothing about this is in the changelogs for the updated version

I can't reproduce this issue on my end. The ghastlings are summoned as normal and fly about at full health.

Yeah getting the same issue currently

Reproducible for sure in 1.0.1, will update in a short while and see if it's somehow fixed

Updated to 1.0.2, new world, same issue

Forge version is 14.23.5.2854 on those, by the way

Changed to a 'test set' modlist of only QoL and Wizardry related mods, Ghastlings are now flying about as intended 🤔
Will check other mods to see what the problem might be.

This issue appears to be something to do with Inventory Pets?

Weird, looks like the lightning that's summoning them is killing them. Very rarely will one survive with really low health.

Right, sorry for the long delay but that information is helpful, thanks. TF spell pack sets the ghastlings to have a second or so of invulnerability on spawn to protect them from the lightning, using the vanilla system to do so. However, I have seen problems before caused by potion core messing with this system, so did you by any chance have potion core installed? If so, others have been able to solve previous issues by disabling a config option for potion core, I think it's called separateInvulnerabilityTimers or something similar.

MC Eternal, the pack I first encountered this on, does not have Potion Core installed. The issue came up when installing Inventory Pets.

Hmm, I thought I'd made them immune to that. I'll have to take a look, thanks.