I am not familiar with such a behavior.
I would try a quick file repair. Then a level 2 file repair. Then another quick file repair.
If the problem persists, you could try transferring to a different new investment account.
If that does not work either, I would consider removing the symbol for the problem investment, rename the problem investment aaB, create a new investment with the old name (possibly starting with A temporarily), and old symbol. The go the aaB investment.
Make a new temporary AddShares transaction (dated before all others), adding a big number of aab shares. Then change each real aaB transaction to the new one. Once no other aaB shares remain, delete the big temporary AddShares.