TAC suspects this bug as the cause of the issue I am currently experiencing. I have seen it in 15.3.? through 156-2.SP5. Currently running 152-4.S7 without issue.
I received an engineering release from TAC with the fix for this bug and was told that the issue will be fixed in official image 15.6(2)SP6 to be released tentatively by the end of March 2019. I have not yet deployed the engineering release, so can't verify that it has fixed the issue.
Has anyone installed 15.6(2)SP8? This bug may have been re-introduced in this version or SP7(didn't install this one). I will be opening a TAC case to try to confirm. Ran fine on SP6 since 2019 and recently installed SP8. I had a trouble call today that had already cleared, but logs and issue description seems very familiar to this bug. There are equal-cost EIGRP routes and route flapping appeared to trigger the issue. This is the same scenario that triggered this bug.