The root cause of this is frequently Android itself, trying to manage your phone's battery life by forcing "low" priority apps to go to sleep, with the end result being those delayed notifications. Fortunately, Android does offer you the ability to configure this behavior on some level, on an app-by-app basis, so that you can be more confident that notifications will be received when they're sent, not when your phone decides you should get them.
Fixing this is relatively simple, and though the Battery Optimization feature may seem a little confusing at first, it really is just a few quick steps to resolve this issue.
Step 1. Go to Phone Settings > Apps > App management > Velox
Step 2. Go to Battery Usage and enable the three settings inside power consumption controls.
To ensure Velox app does not close in the background while using, especially during work hours. Lock the application in the taskbar by following these steps.
Step 1. While the velox app is open, go to App Switcher/App Drawer by dragging the screen from the bottom to the center or the pressing the app drawer/switcher button and you will see the velox app.
Step 2. Click the Menu Button on Top Right of the App > Click on Lock and the application should be locked in the taskbar.