I have had the same problems with Nicehash -> Prohashing several days now, both algorithms x11 and scrypt.
Other pools work, for example miningpoolhub and coinotron, and Prohashing used to work well too, but if you check it now with Nicehash pool verificator there comes a message from Nicehash:
"Pool host: prohashing.com
Algorithm: Scrypt
Resolving pool host prohashing.com... Error: prohashing.com
Your pool is shown as incompatible therefore we encourage you to contact pool operator to make sure that the pool is using minimal/starting pool share difficulty which is compatible with our service (and thus compatible with today's miners), please send them link to our FAQ on this topic:
https://www.nicehash.com/index.jsp?p=faq#faqb3. Thank you!"
Also there is a message in Nicehash front page:
"Pool operators & buyers of hashing power,
We're rising minimum pool difficulties for algorithms id 0 up to including algorithm id 19 due to rising network difficulties of popular crypto coins. Here is a list of all algorithms where first algorithm is id 0, second is id 1, etc. Please make sure that your favorite pools will be compatible with this change. The new difficulties will be doubled current difficulties and will be listed at this page.
The new difficulty will be activated on October 11th 2017 at 09:00 UTC.
Thank you for your using our service and keep on hashing!
Best regards,
NiceHash team"
Links:
https://www.nicehash.com/algorithm
https://www.nicehash.com/pool-operators