Mysql at 100% with queries

Hi,
we have a client with a web page who’s been using Ninja Forms for years now. Last week the website was having issues where some SQL queries where making the machine go to 100% CPU usage.
The queries were:

SELECT Meta.key, Meta.value FROM wp_nf3_fields as Object JOIN wp_nf3_field_meta as Meta ON Object.id = Meta.parent_id WHERE Object.id = ‘199’

As soon as Ninja Forms was disabled the queries went down.

Plugin version 3.6.0

Would anyone know the cause?