discrepancies in calculations

Good morning!
I’ve been struggling for quite some time with what seems like a fairly simple report that should calculate:

1. Hours spent on a client (effort and time spent, broken down into billable and non-billable) for a given month
2. Broken down by teams
3. Broken down by individual team members

All of my calculations come out completely different and don’t match the sums where they should. For example, if the report states that the total time spent on the Auchan client is 892 hours, then the sum of hours per team for Auchan should match this number, but it doesn’t (I’m getting 543 hours). I also did a double-check using “standard” reports, where the total is different yet again, at 552 hours.

I’m not sure what I’m doing wrong, and support tries to help but on the other hand it falls outside their scope.

1. HOURS SPENT ON A CLIENT

Here is a screenshot of total billable / non billable per client in October (effort and time spent). Let's focus on one client (red box).

Here, the total time spent is 892h.

In basic reports: 553h

2. EACH TIME HOURS SPENT ON A CLIENT

Then, analytics for each team:

Effort formula:

Time spent formula:

Total time spent of this team for this client:

The same formulas are for other 4 teams.

In total I have 545h of time spent which is closer to the result I get in basic reports (553h) but still there's a discrepancy.

3. INDIVIDUAL PERSON TIME SPENT ON A CLIENT

Here I have a complete mess.

Let's take my colleague Bartek who on a screenshot above has effort 6h and time spent 3h.

Here he has 22 and 8 💀

The effort formula:

The time spent formula:

I tried with Task Assignee ID but nothing changes.

I really don't know what I'm doing wrong but I really need a reliable reporting 🙁