Hi Paola Gatto 

Sounds like you have a placeholder tag that has not been managed well within the target translations.
Have you run a verification check specifically on tags?

One thing I do which helps clarity area of concern is to take the source file.

• Create new project without TM
• Copy source to target
• Save target as

If it saves, then you know the issue is not with the source file but something that was introduced during translation.

You could also try search for the tag by using the Advanced Display Filter and search for the text in tag content on the source side.
Then see how it had been managed on target side

I hope this helps you identity root cause and that you can resolve it from there
Have a good day

Lyds