Pi was working fine for me today, around that 9:25 AM time when few ppl reported issue, I saw some tick-data blanks.
That would indicate server congestion, I don't think internet connection would be an issue.
Even when logged in, keep an eye on market watch, and observe if the whole window greys out along with your Task manager network window open.
If it does at those times and your internet data is fine, that means Zerodha servers are skipping your requests.