Let me back up if its ok for a second just to connect the dots.
This flow would run anytime the row is modified or a new one is created, so as it relates to the approvals, this flow would trigger (assumed) for prior steps 1 and 2 of the approval, not just for the 3rd, and I only say that because i haven't seen the totality of the approval steps, but the question in my head is
1. Is it getting updated via this flow for the FINAL approval, or for a previous approval and it just stays this way.
So here is my question / thoughts:
A) Can you please go into the flow and, if you are able to identify, the time it triggered for the 3rd approval. Then let's look at the Condition and, for a time you know it should NOT update (aka go to the No side), let's see why it went to the Yes side, because again, either it got set in a previous trigger for that row, OR there is a bug where the 3rd iteration / trigger of this (if that is what is happening) has bad data.
The flow run, from the Details page, open up the flow, let's look at the Raw output of the Trigger, and then also the Condition Inputs / outputs
If these suggestions help resolve your issue, Please consider Marking the answer as such and also maybe a like.
Thank you!
Sincerely, Michael Gernaey