Hi @Anonymous ,
Could you please share a bit more about your scenario?
Do you mean that the canvas app is stuck to the left side of the screen?
Based on the issue that you mentioned, I think this issue is related to "Optimize embedding experience" option within Advanced settings of your App settings.
Please consider turn off the "Optimize embedding experience" option within Advanced settings of your App settings of your app, then re-published your canvas app, then check if the issue is solved.

Please consider take a try with above solution, check if the issue is solved.
Best regards,