[HYDROID Prime is now very broken! And other problems]

In re: the Hydroid issue, a considerable number of people are experiencing it as well. There's another thread on it in the Eidolon bugs forum. It's really annoying at this point, happens fairly often to me.

[Hydroid prime - Tiny. Headless. Useless.]

I'm experiencing the same issue. After using undertow and then attempting to exit, there is a chance I'll become a mini, headless coatless Hydroid.

I'm unable to shoot, melee, run, or interact (save for using abilities except undertow itself).

Never experienced this pre-Eidolons patch.