I reported this issue already one year ago to MetaQuotes but never got a helpful response. Sometimes - don´t ask me when - a simple execution of functions) like iClose(), iTime() or CopyRates(), CopyTime() whatever takes more than 30 seconds until the code-pointer returns. And of course, when you execute several commands in a row, the EA crashes.
It happens with several brokers - only on live accounts - and with several symbols and all MT5 versions. I just never saw it with real futures, but with almost any other. It happens with a local internet connect, with a VPS, with my environment and with environment of customers, very rare, but it happens and only with MT5, not MT4. I already implemented a measurement and a forced termination of the EA, when the measurement detects a timeout (>4 seconds).
This is pretty annoying and I am sure, this is general problem of MT5, not a broker specific.