Advice to making Boba Pearls
I visited some Chinese language websites, and it seems that there really isn't any magic here. Since their recipe is basically the same as the first one you linked to, I won't post any links here. I've never made tapioca balls, but the technique used here is a technique common in Chinese cooking called &quot;hot dough&quot; (tangmian 烫面), which I often use.
The water mixture (syrup?) must be consistent and boiling hot, so boiling the mixture for a while might be a wise choice. Also, stir quickly and well. This might explain why your first two attempts failed: the phrase to remember here is starch gelatinization, and if your water-starch mixture doesn't stay hot enough, there wouldn't be enough gelatinization there.
It's usually better to err on the side of too much water (but of course, not way too much), as you can add starch to get the desired consistency.
Also, you are not supposed to leave it there for 10 minutes; it is normal for the dough to become hard after a while. You are supposed to make the tapioca balls from the dough _right away. Yes, it would be hot, so it would be wise to wear gloves. If you really need to leave it to cool down, covering the dough with a hot wet kitchen towel might help.
Once you craft your bobas, it would be just fine to leave it to harden. It might be wise to cover your bobas with (raw) tapioca powder to prevent sticking.