I would never have imagined this. I just changed out my worn-out 24" Hookworm for a new one, pumped it up to 60 psi, and took off down the road . . . all over the road. All the directional stability of the old bald Hookworm was GONE! The uni rode like the road was carpeted with ball bearings. I must have dropped it six times in thirty minutes (I almost never drop it anymore) and anyone seeing me weave down the road must have thought I was drunk.
I could do with some Pinot at the moment, as a matter of fact. I kept letting air out of the tire along the way, hoping to calm the beast down, but it did not seem to do much good, though it was down to 40 psi by the time I got home. Now I dropped it down to 30 for the next ride. We shall see. Have other people gone through the same circus?
Back in my early days of riding I changed the 50 year old stock tire on a 20” Schwinn after the tube blew out through a hole in the tire. I put on a pointed bike tire, very high midsection and not flat or round, but pointy. It was kind of weird at first but slightly lower pressures helped and I got used to it pretty quickly. Maybe the hookworm has changed, if that’s the case, you might want to try a different tire. I run some kind of Kenda on my Club 24” and I know a guy with a Nimbus 24” that uses a Schwalbe something or other. I don’t have experience with the hookworm so I can’t say if it is squirrelly or not, but seems like it might be based on your report.
I have come to the conclusion that it must have been the residual manufacturing oils on the surface of the tire that made it unrideable. It is fine now. It brings up an interesting aspect of unicycle riding that I noticed from the beginning: how important friction is to this sport. If the soles of my shoes are wet, I can not ride, and of course the tire has to have a good grip on the road. Both are much more critical than would be the case with a bicycle, for example.