Workflow starting with no apparent trigger

Workflow starting with no apparent trigger

Hello,

I've setup a workflow which is triggered when  an account is created or edited. It then check a checkbox state, and when true, it updated related contacts fields. This is the following post: https://help.zoho.com/portal/en/community/topic/how-to-send-email-to-contacts-filtered-by-one-account-field

The workflow ("CRM Push Fleet to contact") behave as normal, when the accounts is edited manually from a colleague. (there is a second workflow "Company has Fleet" handling the Fleet checkbox)
For example, this timeline:


However, since its in place, we have noticed a strange behaviour. The workflow is triggered "automatically", many times a day. I thought may be the synchronization between CRM and Books was the reason, but it doesn't on y regular basis. About 300 accounts have this workflow triggered.. why 300 out of 750...


I checked related contacts to see if the function edits any value. I can't see any entry in the timeline.

How could this workflow be started all alone, with no manual edit ?

Regards