Seems unusual, as the ‘app’ is merely a window into what is happening on the Sonos devices, it’s not actually ‘playing’ anything, just telling the Sonos system what to play, from where.
it does suggest some sort of potential wifi interference between your mobile device and your router, if the data in the linked FAQ doesn’t help, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem from both devices, , and call Sonos Support to discuss it. But don’t post the resulting diagnostic numbers here, they get sensitive about GDPR.
There may be information included in the diagnostics that will help Sonos pinpoint the issue and help you find a solution.
When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.