Seems to be the same as https://github.com/Rudd-O/ledgerhelpers/issues/28 but we had fixed this one a while back :-/ I'll take a closer look.
- Bug#1108809: ledgerhelpers: FTBFS randomly: AssertionError:... Santiago Vila
- Bug#1108809: ledgerhelpers: FTBFS randomly: AssertionE... Marcin Owsiany
- Bug#1108809: ledgerhelpers: FTBFS randomly: Assert... Santiago Vila
- Bug#1108809: ledgerhelpers: FTBFS randomly: As... Marcin Owsiany
- Bug#1108809: ledgerhelpers: FTBFS randomly... Marcin Owsiany