Sounds like you are on NBN HFC. If so, yours appears to be a common problem with (NBN) HFC. Optus probably cannot do anything to improve things for you.
The real blame lies with our beloved politicians who decided that they could roll out an NBN quicker/faster/cheaper rather than a mostly FTTP NBN. It's not very quick (original promise was for 2016), definitely not faster, and appears to not be (much) cheaper.
Restarting the modem usually restores the connection but then it will just disconnect a few minutes later anyway. And for the number of times it drops out, I would say anywhere between 5 to 10 times during the span of 3 PM - 5 PM. And for the technology, I'm not too sure sorry.
Good advice, Paquicamus! Glad to hear a change of modem resolved your issue.
Let us know how you go after the tech visit, RedgeRuiter.