[MySQL 5.5.25] Can't upgrade from Antelope to Barracuda (no replies)

Hello,

I am having the following errors when trying to add columns to one of my tables:

"Error Code: 1118
Row size too large (> 8126). Changing some columns to TEXT or BLOB may help. In current row format, BLOB prefix of 0 bytes is stored inline."


This is due to the fact that I'm having 15 LONGTEXT columns. And that all of the columns have data in them.
I'm currently using Innodb, and my tables have been created using the Antelope file format.


To help me avoid the "row size too large (> 8126)" errors,
I am trying to change my tables to use the Barracuda file format,


I have already changed the following configuration keys:

innodb_file_per_table=1
innodb_file_format=Barracuda
innodb_file_format_max=Barracuda


My initial tables still use "Compact" row format.
I read that I need to alter the existing table to use "Dynamic" or Compressed".


Neither of the following ALTER requests work:
ALTER TABLE myTable ROW_FORMAT=DYNAMIC;
ALTER TABLE myTable ROW_FORMAT=COMPRESSED;

When trying these ALTER requests, I get:
"Error Code: 1118
Row size too large (> 8126). Changing some columns to TEXT or BLOB may help. In current row format, BLOB prefix of 0 bytes is stored inline."


Which means that I get the error that I'm trying to avoir by doing this ALTER request.
Even the "Optimize table" request doesn't work, I also get this error.

Even after I have tried emptying EVERY LONGTEXT columns I still get that error.


Do you know why?
What did I do wrong?
Why can't I "transform" my Antelope tables to Barracuda tables.
Thank you in advance.

Kind regards,
Romain.