Yup, it is a problem.
I remember the time I got 41 separate emails in one day for the same assignment at 41 different locations of the client in my area. Here is what I did.
First, I emailed a higher-up of that company to suggest 41 emails is too many. They backed off for a while. When I got about 18 in one day (if memory serves), I set up an email filter. All emails from that scheduler got put into a folder that I look at only when I have the time. I have about 60 filters for mystery shopping emails. These are a variety of shops of shops I am not eligible for or prefer not to do. Some filters move all emails from designated MSPs out of my inbox. It is based on my personal preferences.
Back to the 41 emails in a day shop. Without the reminders, I checked the job board less frequently, resulting in less assignments. It was a shame because I liked to do that shop. Later, the shops ended. Maybe the client was unhappy with the service from the MSP. I know I didn't need all those emails. One a day is quite sufficient in the normal course of events.
Happily shopping Rhode Island and nearby Massachusetts and Connecticut