What are the implications of ETFs lending out their holdings?

I’ve noticed some ETFs describing how they can lend out their holdings, usually for some amount of collateral (cash, U.S. government securities, stand-by letters of credit, etc).

If we take GDX, for example, it looks like they’ve loaned out up to 1/3 of their holdings 2020 YTD, which seems high. It’s made clear that these lending activities can lead to loses for the fund, e.g. if the borrower defaults and the posted collateral isn’t enough to purchase back the securities due to capital appreciation in the meantime.

Another risk I’ve seen in prospectuses is when the value of the collateral or investments made with the collateral drop in value. I haven’t really seen any descriptions on how collateral funded investments are made, governed, etc.

Besides the above, are there any other risks typically associated with these lending activities? Are there any other implications I should be aware of?

Other ETFs, e.g. VEU, don’t make these lending activities – if any – as clear. Besides reaching out to the issuers, where can I find out more about any given fund’s lending activities, how they’re managed, etc?