Is TopStore VIP safe? Yes, it is safe and secure, there is no significant threat to your device.
Why do apps stop working often? This is due to revokes. TopStore uses enterprise certificates to sideload these apps to your device, Apple regularly checks for certificates and once they find their enterprise certificates are being misused. They immediately revoke certificates. When revoke happens, many apps may stop working as one or many apps can be under one certificate. Fix is use anti revoke apps that are available in the market or use VPN which gives you a secure and private connection.
Why some apps are not working on my device (none revoke situation)? This is because the app you want to download onto your device is not compatible with your device. There are some apps which are only compatible with iOS 11 and above. If your phone’s iOS is below iOS 11 then those apps won’t function on your device.