If you use mobile data and have lots of back-to-back calls during your working hours, sometimes, you will notice that Salestrail doesn't log your calls immediately after you hang up. No worries, no data is lost, they just come with a delay, which could range from 10 minutes to a few hours. Read more about it here.
Mobile devices prioritise calls, hence, your data connection "weakens" when you are on a call (especially if you're using Edge or 3G). If your device and phone provider support VoLTE, it might help in this situation. If not, there are chances that Salestrail doesn't get sufficient internet connection to log the calls immediately.
Another possibility is your mobile device has Internet Hotspot turned on, which can make the data connection spotty.
Be patient: give Salestrail some time to process the data.
Let your phone rest for awhile.
Make outbound phone calls from Salestrail instead of over-using your device's keypad.