Cash flow statement - only one year wrong?

Help highly appreciated! I‘m currently in a recruiting process and have a week long business case to model. Only had public balance sheets and P&Ls available, entered most data (left out some minor accounts and took totals, for example for intangibles etc) and calculated cash flow statements. For three out of four years they are perfectly correct and match the change in C&CE, one year has a significant difference to the actual change in cash (around 10%). All formulas are the same, data input is correct. Have spent hours on fixing it, cannot find the error. Difference is nowhere to be found, obviously checked all differences in BS accounts in original documents with before and after accounts, all P&Ls (also all accounts I left out). Data must be correct since it was audited and filed with authorities. I even tried solver to combine any numbers into the missing cash. Any advice on how to find the mistake? What would be a common error? Otherwise, how to communicate this? Thank you!