Bilibili downloading only first part of video

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[x] Searched the bugtracker for similar issues including closed ones
[x] Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

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[ ] Site support request (request for adding support for a new site)
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If the purpose of this issue is a bug report, site support request or you are not completely sure provide the full verbose output as follows:

Add the -v flag to your command line you run youtube-dl with (youtube-dl -v <your command line>), copy the whole output and insert it here. It should look similar to one below (replace it with your log inserted between triple ```):

youtube-dl -v https://www.bilibili.com/video/av7850279/
[debug] System config: []
[debug] User config: ['--no-mtime', '-o', 'C:/Users/User/Music/%(title)s.%(ext)s']
[debug] Custom config: []
[debug] Command-line args: ['-v', 'https://www.bilibili.com/video/av7850279/']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2018.05.01
[debug] Python version 3.5.2 (CPython) - Windows-10-10.0.16299-SP0
[debug] exe versions: ffmpeg 3.3.2, ffprobe 3.3.2
[debug] Proxy map: {}
[BiliBili] 7850279: Downloading webpage
[BiliBili] 7850279: Downloading video info page
[download] Downloading playlist: 2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel
[BiliBili] playlist 2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel: Collected 6 video ids (downloading 6 of them)
[download] Downloading video 1 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-1-80.flv?um_deadline=1525235407&platform=pc&rate=387600&oi=1279479545&um_sign=130005cc13f098c631b4633152d85e9b&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] Destination: C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv
[download] 100% of 74.17MiB in 02:46
[download] Downloading video 2 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-2-80.flv?um_deadline=1525235407&platform=pc&rate=426700&oi=1279479545&um_sign=ffb8236f1ab1daa5fd75ab5450f2c887&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv has already been downloaded
[download] 100% of 74.17MiB
[download] Downloading video 3 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-3-80.flv?um_deadline=1525235407&platform=pc&rate=387600&oi=1279479545&um_sign=6b0be6c6e6d00cf2e36e96c79e73ac38&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv has already been downloaded
[download] 100% of 74.17MiB
[download] Downloading video 4 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-4-80.flv?um_deadline=1525235407&platform=pc&rate=418200&oi=1279479545&um_sign=6329ca23bbdd5c2bba8fd395fd06c246&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv has already been downloaded
[download] 100% of 74.17MiB
[download] Downloading video 5 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-5-80.flv?um_deadline=1525235407&platform=pc&rate=453900&oi=1279479545&um_sign=22281ff123608ad92fba13e69617a2ee&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv has already been downloaded
[download] 100% of 74.17MiB
[download] Downloading video 6 of 6
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/06/40/12894006/12894006-6-80.flv?um_deadline=1525235407&platform=pc&rate=498100&oi=1279479545&um_sign=ed9d9623d012d86eb9df9ac5942a09c3&gen=playurl&os=cos&trid=fc6b72cac3874213a1ace606123bade0'
[download] C:\Users\User\Music\2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel.flv has already been downloaded
[download] 100% of 74.17MiB
[download] Finished downloading playlist: 2017年维也纳新年音乐会 Neujahrskonzert 2017 mit Gustavo Dudamel

Description of your issue, suggested solution and other information

Video is ~33 min long; only first ~5m40s is getting downloaded.

Many other issues (including closed ones) seemed to have similar issues with Bilibili downloader, but this problem appears to be slightly different. It recognizes that the video has multiple "parts", but it tries to re-download the same part 6 times instead of downloading all the parts. Then it just says "has already been downloaded" for parts 2-6.

ytdl-org / youtube-dl