I'm use sandisk uhs-1 to,I buy it two years ago.it's very smooth if not connected to WiFi network. When I connected to WiFi it start laggy and sometime rebooting. But overall it's not much problem. I'm install 67 app on it maybe sometime it's laggy or sometime reboot because too many app running at the same time.
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I think it may be related to too many apps. Maybe check if your installed apps are network features related or not.
When you connect to WiFi, system will broadcast an event that WiFi is connected.
Then all installed apps (no matter background running apps or not) might receive the WiFi event (if apps register themselves to receive the WiFi event) to do the corresponding tasks.
Since many tasks may be triggered at the same time, it has the chance to lag your phone.