I’ve got KiCad V5.1.6 and run on Linux, and on my system the time.
I can verify it generates a .pos file, but I have no Idea what the difference is with what JLCPCB expects.
The difference is probably easy to spot if you can find an example file at JLCPCB’s website, or if someone with an older KiCad version is kind enough to post an example here.
I did find a few old open source projects on my HDD, but they seem to be the same format KiCad generates now, and were probably made without that “With INSERT attribute set” option.
Nevertheless, here an example of an older file in ASCII format:
### Module positions - created on 11/21/19 09:54:47 ### ### Printed by Pcbnew version kicad 4.0.7 ## Unit = mm, Angle = deg. ## Side : top # Ref Val Package PosX PosY Rot Side C1 C_22n C_0603 36.8500 139.1000 270.0000 top C2 C_22n C_0603 11.8500 139.1000 270.0000 top C3 C_15p C_0603 52.9210 127.5825 180.0000 top C4 C_360p C_0603 50.1270 139.9095 180.0000 top C5 C_15p C_0603 27.2670 127.5825 180.0000 top C6 C_360p C_0603 24.1000 139.9000 180.0000 top ... ** End