Some error in ERA but very difficult to make a diagnos

Hi

I have several error in ERA in this function

(:SecondTimeUtc) function FctTimeUtc(i,utc,Tableau,ForceLic) {




var timestamp = Time.now().value().toDouble() + 3600 * utc;   // utc is a signed  float number example 1.0  or 3.5
timestamp = timestamp.toNumber();

timestamp=timestamp % 86400;
var hourutc = timestamp / 3600;
var minutc = (timestamp / 60) % 60;

.....

Sometimes In era I have

Invalid Value 

Error Name: Invalid Value
Occurrences: 1
First Occurrence: 2020-12-15
Last Occurrence: 2020-12-15
Devices:
Forerunner® 945: 5.50
App Versions: 7.5.1
Languages: spa
Backtrace:
GenView.FctTimeUtc:3723

or 

System error. 

Error Name: System Error
Occurrences: 1
First Occurrence: 2020-12-15
Last Occurrence: 2020-12-15
Devices:
fēnix® 5 Plus: 14.00
App Versions: 7.5.1
Languages: deu
Backtrace:
GenView.FctTimeUtc:3723

....

How can I diagnos this issue, because on my watch I don't have any problem

Thanks  Didier