Index corruption with import tablespace

[Marcel van Brakel]

Due to some data loss after a misplaced truncate table, I tried to restore an .idb file using the following procedure:

alter table x discard tablespace
replaced the x.idb file with one from our veaam backup
alter table x import tablespace

but this gives me the message:

Error Code: 1817. Index corrupt: Externally stored column(52) has a reference length of 3 in the cluster index PRIMARY

The column 52 is a column of type longtext.

This is innodb running on a Windows server.

Anyone have an idea of how to proceed? Or another method of restoring the content of the .idb file?