Hello,
Yes, it is. According to the WordPress documentation, the taxonomy slug
must not exceed 32 characters and may only contain lowercase alphanumeric characters, dashes, and underscores
https://developer.wordpress.org/reference/functions/register_taxonomy/
Can you please change it to a sample slug like my_taxonomy_slug
and check this issue again? You can also deactivate all plugins except Meta Box, MB extensions and switch to a standard theme of WordPress and see if it helps.