Hi Timo,
We’ve just published a new version of Needle Engine that has a fix for WebXR image tracking on iOS: Releases & Changelogs - #206 by needle-bot and submitted an update to the AppClip (Needle Go) to Apple which should be available within the next 24-48 hours. The AppClip will automatically update when it’s available on your device but I’ll also make sure to update this post here when we got confirmation from Apple.
Both of these updates combined should fix the issue with image tracking requiring a second start.
We’ll also update Blender with the latest version of Needle Engine later today so you can simply update your Blender addon version.