Verify observation parsing
It seems the format of wdcgg observation parsing has changed over time and has not been consistently updated for the other observation type, namely the "verify" observation parser.
Commit 9d0514eb basically changed the format of the wdcgg observation dataframe so that instead of having the "time" as the index, it has instead a column called "date".
Commit 30602248 made use of this in the standard measurement plugin . The issue is that it breaks the verify observation parser, which does not have that column, and still uses the "time" as index. Note that a similar line was deleted in the wdcgg obsparsers in the commit 9d0514eb
Simply adding df['date'] = df.index
at the end of the verify observation parser would probably fix the issue, but I can't definitely say it is the right solution.