Depending on the firmware version you are using you might want to try toggling the Client Balancing setting in whichever RF profile the APs are associated to, check under Wireless > Radio Settings and click into the RF Profiles page and edit the RF Profile they are assigned to.
While on that page, also make sure you are following other common best-practice settings, such as disabling the lowest couple of bit rates on each radio (perhaps try a minimum of 12Mbps) and limit the transmit power to better match the clients. If you look at the overview page you can see which AP radios are transmitting at which power levels.
You may need to take a look at your AP placement and do a site survey walk through to make sure the coverage and overlap is appropriate. It is always the client's decision to roam to another AP. If you are leveraging 802.11k/v the APs can try to influence a better informed decision but it's still the client's decision, and you can certainly have a client in a room with an AP but still associate to an AP in the next room or two rooms away, that is not too uncommon.
Toggling client balancing on/off for a period of time and noting any change in behavior could be a useful data point. Then I'd open a ticket with Meraki Support and have them look over your config and do a firmware scrub for your specific version and they might also suggest a better alternative.
