Invalid GPS coordinates on GoPro 6

[highsource]

I am trying to export a GPX track from an MP4 video filmed on GoPro 6.

Somehow I'm getting invalid coordinates. I see several problems which appear on the exported GPX track - but which I don't see on the GPS gauge in Quik.
I will create a separate issue per problem.

First problem is that I'm getting completely off-the track coordinates. Here's a example:

The video is filmed in Germany (around 8.663, 50.232). A few first points on the exported GPX track lie north of Canada (-128.4998971, 80.8641778). Also the elevation for these points is exported as 20841.167 (in reality should be around 202).

Quik seem to show this track correctly:

The complete video is ca. 3.4GB so I can't reasonably share it. I also don't know how can I cut it while keeping all the streams including GoPro MET.

Below is the .bin file I've exported from the video:

GX030039.zip

This is how I've exported it:

ffmpeg -y -i GX030039.MP4 -codec copy -map 0:3:handler_name:" GoPro MET" -f rawvideo  GX030039.bin

Below is the (zipped due to GitHub) GPX track:

GX030039.gpx.zip

Exported using:

gopro2gpx -i GX030039.bin -o GX030039.gpx

Invalid points look like:

			<trkpt lat="80.8641778" lon="-128.4998971">
				<ele>20841.167</ele>
				<time>2018-09-29T10:20:53Z</time>
			</trkpt>
			<trkpt lat="80.8641778" lon="-128.4998971">
				<ele>20841.167</ele>
				<time>2018-09-29T10:20:54Z</time>
			</trkpt>

First valid point:

			<trkpt lat="50.2319754" lon="8.6630605">
				<ele>202.121</ele>
				<time>2018-09-29T10:23:51Z</time>
			</trkpt>