overflows can be a little sketchy. I second the statement that the mag24 may be too much pump for them depending on head pressure. I hope you put a valve on the return line so you can turn it down if needed.
Please prime the overflows before you plug it in.
Are both of the overflow inlets at the same height? If so, you may have issues with one of them constantly losing syphon and then the other not being able to keep up. Make one inlet slightly taller than the other. The short one will run under full syphon and the taller one will take up the slack.
Best of luck.