I had a hard time to reproduce the SameSite cookie issue between multiple Chrome browsers. The reason, as it would seem, was the the Default setting of the SameSite flags are NOT neccesarly the same between Browser instances.
My Chrome on my PC reported “Cookies without SameSite must be secure” to be enabled with default checked, while on my collegues PC, it reported as being disabled with default checked.
This made it impossible for him to reproduce the issue that I had an easy time to reproduce. We had the exact same version of Chrome and were both using Windows 10, although not exact same version of Windows.
Lesson learned: Do not trust the Defaults in Chrome when debugging, enfore the same settings across instances.