I guess the issue is whether the part of the flight over Netherlands was rendered 'illegal' by carrying a PLB.
Nothing whatosever illegal in carrying a PLB Steve.
[/pedant]
I believe the general rule with insurance is to question whether the alleged failing contributed to the claim.
If an uninsured driver crossed the central reservation and hit the front of your car your claim would not be invalidated by the fact that your rear number-plate light was not working and your car was therefore technically not roadworthy.