54 kg of fentanyl is an insane amount to have all in one place.

Just to put it in perspective:

• Assuming the lethal dose (LD50) of fentanyl in humans is similar to in mice (probably a good assumption), it is 7 mg / kg of body weight by injection. Assuming an average body weight of 70 kg, 54 kg is enough to kill 110,204 people.
• Apparently for opiate tolerant people (e.g. addicts), the therapeutic dose for strong pain relief is 12 μg / h, so in a month, an addict wanting to stay dosed up the whole time might use 8.64 mg total. 54 kg is enough to supply 6.25 million addicts for a month.
• According to a UNODC estime, in 2023, there were about 60.3 million opioid (including opiate) users worldwide, including prescription drug users. So that one stockpile could supply 1/10th of the world’s opioid users for a month. It almost certainly isn’t for supplying prescription drug users, and many opioid addicts likely try to avoid fentanyl, and there are other competing sources - so 1/10th is a lot.

I’m not sure why they’d stockpile so much in one place, given they apparently have the capacity to manufacture more - unless they were planning to use it to kill people (see: they also had a weapons cache and explosives) instead of to sell as a drug. Or perhaps the 54 kg is an exaggeration and includes packaging and so on.