JBOK (just a bunch of keys) wallets generate the keys independently from each other.
In contrast, HD wallets are hierarchical and deterministic: They need a seed (e.g. a couple of words) and can generate the keys with that. This allows HD wallets to have a convenient backup mechanism: Just store the seed (e.g. 12 words with Trezor Model T, 25 words as with Trezor Model One, 24 words, 12/24 words with Exodus, 12 words for coinbase, 12 word for Electrum). I'm uncertain if any of those wallets use it, but the procedure is described in BIP 32 / BIP 39 / BIP 44.
Every single wallet I've checked is a HD wallet. Do JBOK wallets (still) exist? Do they have advantages over HD wallets?
For example, I could imagine that JBOK wallets are more secure because they are simpler. Are there any known issues that come from the way the keys were derived / errors in the implementation?