There have been several changes and fixes to the mobile module since the version you are running. One of these issues had to do with idle vm’s staying open when they shouldn’t. Currently the LTS (long term support) version of Ignition is 7.5 and bug fixes are being made to this branch and will continue to be made for several more years. I would suggest upgrading to the latest 7.5.11 if your license allows because it is very likely that this issue has been resolved.