Weaponswap not properly checking for ailment immunity (Crystallised Immunities)

https://medal.tv/games/path-of-exile-2/clips/m2vivpS0KnQtAhseT?invite=cr-MSxwTjcsMjU1NDI4OTQ3&v=30

Visible starting at ~0:21 in the video.

This is an acquaintance's reverse chill Stormweaver. He has Crystallised Immunities, but it is only providing Ignite immunity on his combat (bow) weaponset. His other weaponset (Thunderstorm swap) does not have enough red gems.

When he casts Thunderstorm at 0:21, he self-ignites off the Shackles reflect which is expected, but you can see he swaps back to his bow to continue DPS'ing right after, yet the Ignite continues to burn him down until it expires. To my understanding, he should have Ignite immunity as soon as he swaps back to his bow, so some kind of check on weaponswap appears to not be occurring.