The biggest issue is in finding people to work with it. If you're hiring React developers over web developers, they will probably struggle more with SolidJS's differences from React, in part because they just look so similar that there's more to "unlearn". But most web developer (i.e. anyone who can understand beyond just the confines of their favourite framework) should find it relatively easy to understand what's going on.
I guess technically that part of the application didn't scale so well in SolidJS, but it scaled a lot better than it would have in any other framework, and we got to delay writing the engine "properly" until we'd already built everything else and got it running with real users in production.