That's not quite right.
Yes, drop the table "wp_toolset_relationships" from the database, and Types will recreate it. It occurs to me now that you will also need to drop the tables "wp_toolset_associations" and "wp_toolset_connected_elements" (which will also be recreated).
You will lose any existing records of connected posts (which includes entries in repeatable field groups), but—as I said in my previous reply—I don't see any alternative because of the corruption of the wp_toolset_relationships table.
(I would encourage you to try returning to a prior backup, in case you have one from before the problems with that table arose, but you say this has been happening for months, and that may not be an option.)
You also need to delete the custom field groups which include repeatable field groups and recreate them. Data about custom field groups are stored as posts (post type wp-types-group) in wp_posts, with corresponding entries in wp_postmeta. Because of the problems with the database tables, you cannot delete them using the UI, you must delete them directly in the database.
So, for each custom field group that has repeatable field groups, edit the field group.
Take a note of its ID (from the URL), and take a note of the fields that make up the field group so that you can recreate it manually.
To delete the field group, delete the post with that ID from wp_posts, and delete all entries in wp_postmeta with that ID as post_id.
Do that for each field group that contains repeatable field groups.
Now recreate these deleted field groups. You don't have to redefine the custom fields, when you click the Add New Field button you can then "choose from previously created fields" and you should be able to locate the previous field definitions and use them in the new custom field groups.
(You won't be able to recreate the repeatable field groups, you will essentially be making them as new.)
During the above you won't have deleted the custom field values from your posts. If you set up field groups in the same way as before, re-using your previously created fields, then when you complete the process if you edit a post that uses these fields it should show the field values as if nothing has happened. The different will be the values for repeatable field groups. These are lost and will need to be added again.
Needless to say you should have a backup before you start, and if there is any part of the above you are not sure about, do please ask.