Also my own report (with video and screenshots) - [Reported] Lycanthropy Gem caused softlock when spellcasting vs. single opponent
Some complications:
1 - You should match the special gem in a way that grants an Extra Turn so that you can spellcast while it is still homing.
2 - Special gems seem to home in on their target at randomized speeds, so the time window for the above (i.e. ability to reproduce) is unpredictable.
Per my hypothesis above, it seems like when you cast a manual-target spell, anything that triggers an update to a target’s status (like Ironhawk’s third trait vs. a Submerged target) somehow removes them from the internal list of eligible targets for that spell, which is a BIG problem when it happens (even when it does not happen often). In all these videos (but particularly the last one) you can clearly see that the affected troop is highlighted as a target UNTIL the special gem actually hits them.
Naturally, this problem did not occur until the implementation of special gems and Ironhawk’s release. And it wouldn’t be an issue at all if we could just cancel out of a spellcast in the first place.