Issue with a spell + trinket macro

A macro I never really had issues using was

/use (trinket here)
/cast (spell here)

If the trinket was up, it would do both.
If the trinket was not up, it would just cast the spell.

However, I’m not able to do this with https://www.wowhead.com/item=204714/satchel-of-healing-spores

The macro is:
#showtooltip Satchel of Healing Spores
/use Satchel of Healing Spores
/cast Power Word: Shield

Except it just uses the trinket and not PW:S.
If the trinket is on CD, it tells me the item is not ready yet.

I’m confused since it’s the exact same macro I’ve always used.

I also have:
#showtooltip
/use Conjured Chillglobe
/cast Shadow Word: Pain

And it works fine… what I’m missing here?

That trinket is on the GCD so it can’t be combined with anything that’s also on the GCD.

GCD 	1.5 seconds

Whereas Chillglobe isn’t.

GCD 	0 seconds

I am ashamed of this topic, but thank you.