With the proma 150 thc, the arcOK signal provides a slightly different function.... within the software setup of the proma, you set the voltage that the arc Ok signal changes state... the intended function is the same, but not quite"arc transfer", ie transfer from HF arc to cutting arc, so if you set the voltage within the proma too low, or close to the cutting arc, motion may not begin until the voltage drops below this set "thc Ok" voltage.
The problem that I expect is being experianced is because your setup is wrong and the torch is crashing into the plate, the proma stopped sending the THCUp signal, until the THCOK signal is restored, and because the cutting voltage has gone so low, it has to wait for it to rise before initiating the THCUp signal after the THCOK signal is restored.
Solution.... wire up the thc the way it is intended to operate, with the THCOK back to the c11, along with the THCUp and THCDn signals. Make sure the settings inside the proma 150 are correct for your setup. And then tune your machine so that the thc responds correctly and quickly enough that the torch is not crashing into the material.
If you can afford a hyperthem 125, I cannot see why you are using such a low cost torch height controller, if I were you, I would look for something better (by which I mean faster, as the proma uses relays inside of it), and with closer control (the proma has a minimum headband of 2 volts)).
There are a few about, like the neuron thc (not the mini).
Thc will improve your cut, but only if it is fast and accurate and your z axis can move fast enough.
No I don't work in the industry or for neuron.... there are others about too, like candcnc, month (po-mo/ Denis), and Texasmicrocircuits, and more too... just look for those that run high resolution and high speed sampling.... some plug straight into the hyperthem using the correct CPC plug / connector.
Good luck