That’s very strange, because even Chuwi says that H3 and H6-pens are incompatible because they use completely different digitizers in the screens (see this thread).
If your Ubook now works with an H6-pen, the original pen included probably wasn’t an H3. From the previous thread there are older Ubooks which work with H3 (SN before 20 05) and newer models (SN after 20 05) that work with H6. Both shouldn’t be possible…
Based on my experience: I bought my Ubook Pro at the same time as and “old” Hi10X for my wife. The H6 pen (Ubook Pro) does not work on the H10X, the H3 pen doesn’t work on the Ubook Pro. The H6 does use the same technology as the Surface pens (later generations, N-trig based) so it does work on all Surface-compatible tablets. H3-pens don’t.