Inaccurate Distance on Road Bike activity

Fer said:

I had a problem with the cadence sensor (connected by ANT+) that did not connect and I did not realize it until I got home. Could this be one of the factors?

The cadence sensor is not a problem, but the speed sensor is. Either it was not connected part of the ride, or it is not calibrated. I do not see any cadence sensor connected at all in this activity. The speeds sensor was connected, but I cannot see whether all the time, or only a part of it:

Thank you very much, you gave me an idea of where I have my problem. I bought these sensors on aliexpress (a pack of 2 units) and they are multifunctional, the same sensor can be used for speed or cadence, but not at the same time. I lost one sensor and the one I still have is attached to the crank to use it in cadence and also in the watch, even so, sometimes in the watch the speed option appears available. To be honest I didn't check which connection I was using, I just made sure it would connect and started riding. While riding, the clock would sometimes show 6~9 km/h, which seemed strange to me as I was going at a much higher speed.
Now it makes sense to me: The crank was measuring speed and not cadence. This makes me think: Is it possible in Garmin connect to choose the source of the speed, to overwrite the sensor information and choose the GPS one?