Unhandled Exception cause?

Can anyone help me understand how the second line(below)  cause an "Unhandled Exception" error?

for (var i = 0; i < priorSpeeds.size(); i++) {
    var value = priorSpeeds[i];	

This error was reported via ERA, on three occasions, and two devices:  F6 Pro and F6X:

Error Name: Unhandled Exception
Occurrences: 3
First Occurrence: 2020-08-22
Last Occurrence: 2020-08-29
Devices:
    fēnix® 6 Pro / 6 Sapphire / quatix® 6: 11.10
    fēnix® 6X Pro / 6X Sapphire / 6X Pro Solar / tactix® Delta Sapphire / quatix® 6X: 10.10
App Versions: Beta 3.8.8
Languages: eng
Backtrace:
    Engine.dispData:581
    Engine.GPSData:1686