Thanks for confirming your copy is clean. That said, I think that will make this harder to reproduce/get any more info on. If this is really happening on a clean copy of mIRC, I feel like you probably have corrupt data on your OS, or faulty hardware. mIRC may be slow, but it's probably one of the most stable programs I've ever used. I've actually never seen mIRC crash randomly without malicious external input (exploit) or a faulty script. Not once. In over a decade.
Are you doing anything specific around the time of the crash that might help diagnose the problem? Does it happen around a preset time after starting the client? If it's really just "random", it's more likely your OS than mIRC, I think.
Do you have an anti-virus program running? If so, try disabling it to test if this continues to happen. Your AV might be messing with the client.
