Column index in source frame inhibits to_timeseries

Bug report

Created the following gist to show some funky behavior when using frames that have been returned from LSST DM's butler, which has a columnar index:

If the index is set to some source id, loc fails in the to_timeseries call.

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[x] I have described the situation in which the bug arose, including what code was executed, information about my environment, and any applicable data others will need to reproduce the problem.
[x] I have included available evidence of the unexpected behavior (including error messages, screenshots, and/or plots) as well as a descriprion of what I expected instead.

lincc-frameworks / tape