Same problem as others, Mitel 5624 WiFi SIP phones, Meraki MR42 access points. Phones worked fine with our old Aruba AP105s but after "upgrading" to these new Meraki access points the phones would stop responding after a very short period of time (much less than the 5 min idle timeout). Tried every suggestion given in this forum with no change. Solution that was finally found after going back and forth with Meraki/Cisco & Mitel support was to upgrade to the newest BETA firmware for the MR42 (26.2). The devices shipped with 25.13 which under knows issues in the release notes states "Condition under investigation that causes VoIP RTP packet loss (MR42/MR52/MR53)", problem has completely gone away after upgrading to 26.2.
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