What are some issues with ETN Commodities Indexes?

I am thinking of buying, two ETNs in Commodities Metals (Copper, Nickel). I am curious of risk factors for these.

1. Besides Barclays Bank going bankrupt during a market crash with unsecured ETN debts, and
2. slight difference between spot price due to contago/backwardization,

Is there anything else I should be aware of ?

I see lot of articles on ETNs and risks, however in the resource articles listed, they are totally different products related to Mortgage, and redemptions etc.

Just curious if anyone is familiar with these products. Currently reading through the 200 page prospectus.

JJN - iPath Series B Bloomberg Nickel Subindex Total ReturnSM ETN 

https://www.ipathetn.com/US/16/en/instruments.app#/details/341631

or

JJC - iPath® Series B Bloomberg Copper Subindex Total ReturnSM ETN

https://www.ipathetn.com/US/16/en/instruments.app#/details/341625

Resource articles:

https://www.forbes.com/sites/rickferri/2012/07/12/investors-warned-about-etn-risks/

https://www.schwab.com/resource-center/insights/content/exchange-traded-notes-the-facts-and-the-risks