@Pamela Lincoln ,
Hopefully you didn't pay for the service as the problem was not fixed.
Usually when a circuit breaker trips it is due to higher than rated current flow through the breaker.
An example of this being caused by a coffee maker could be due to the heater element insulation breaking down and touching the metal frame of the coffee maker. Effectively a short circuit which will cause excessive current to flow and trip the breaker.
There are numerous places in a coffee machine where due to component failure or insulation breakdown this can occur. Especially as water is present, water being not good around electricity as it conducts, perhaps where you don’t want it to
If it was serviced correctly and the problem was told to the repair person they should have tested for this or tried to make it happen if it didn’t when they serviced it.
Admittedly if it is intermittent then this makes it harder to find but that's what repair work is all about.
Finding the cause of the problem and fixing it I mean. Sometimes it is not straightforward or easy and can take a bit of time ;-)