Adding Virtual Column after column x is very slow

In our environment, we usually add and drop generated columns every now and then. There is a very large table in the database with more than 3 million rows and adding/removing column was extremely slow. We opted to change the generated column from STORED to VIRTUAL, so that it is instantaneous. However, we hit another road block: When we try to add the VIRTUAL column after a certain column (I believe this is due to application logic) e.g. AFTER ColumnX, the speed is extremely slow again. It takes more than 4-5 hours to just add the generated VIRTUAL column now. Why would adding the virtual column without AFTER clause be instantaneous while adding AFTER clause slows it to a crawl? Database: MySQL version 5.7 Table rows: 32,636,254 ALTER TABLE mySchema.myTable ADD COLUMN MyColumn VARCHAR(50) GENERATED ALWAYS AS json_unquote(coalesce(json_extract(int_data,'$.Item.IRefNum'), json_extract(m_dt,'$.refId'))) Virtual AFTER ColumnX;