Correcting beginning balance

I do bookkeeping for a non-profit entity.  QBO was set up by someone else two years ago and I inherited.  I have reconciled the accounts for the last two years and this last month when I started to reconcile my beginning balance was off.  Could not track down the problem but it appears an entry was deleted but could not identify where.  I un-reconciled all the way back to January 2018 (beginning of our books in QBO) and it appeared wherever the problem came was solved when I re-reconciled five months.   I am rolling right along and reconciling again and I have the same issue but different amount this time.  Keep in mind I just reconciled 5 months straight with correct beginning and ending balances.  Again cannot identify the problem.  Took the account back to the beginning again but now when I open the reconciliation my beginning balance does not match the opening equity.  I have deleted the opening equity and re-entered but still cant balance because I get the error message that my beginning balance is off.   I literally cannot go back any further in QBO.  So why would the very first bank reconciliation beginning balance not match the opening equity amount?  What other area or number would cause a difference??  Why have I been able to reconcile perfectly for almost two years and then suddenly have a discrepancy in the beginning balance???