That is very strange. HEre are three scenarios and suggestions
1. Are there more power query transformations after the remove duplicates? If so, do you think the duplicate came in on one of those steps? Quite often I've seen situations where a merge query happens and depending on the type of join, it creates a duplicate. You could maybe move remove duplicates at the end if this is the case
2 You could troubleshoot the particular datapoint giving you the issue. Make a matrix, on the rows, throw in the unique column, and in values, throw in the count of the unique column. Sort descending by count and see which value has a count of 2. One you know which datapoint is giving issue, go into power queyr, after remove duplicates, filter out that particular value, then go through all other power query transformations and see on which step the duplicate shows up
3. It's highly unlikely, but it maybe inconsistency in text that power query may be ignore. If the column that shuould have 222 unique entries is a text column, make a copy of that column, text tranform and trim and clean. Remove duplicates from the cleaned up column and see whether the new column gives you the desired unique values. If so, do the same text transformations on the columns which has a relationship with this table.