Edge 540 not recording in 1 second mode ?

Hello,

Symptoms : 

Data screen sometimes stuck for 4-5 seconds for 10s power, 30s power, distance, HR but NOT for time. Found it strange and thought of a sensor/display issue.

Discovered some speed spikes on Strava and then by zooming in i found jumps in GPS position.

Investigation :

I thought smart recording was set to on but actually this option does not exist anymore on edge 540 it seems.

I had a look in the FIT file and found that indeed there are gaps in recordings (see image below).

Defective unit ? normal behaviour ? Firmware issue ? I used it for one year and didn't have this problem at the beginning.

https://connect.garmin.com/modern/activity/17259955507

Thanks !