Fix a wrong computation when several messages (>=3) for the same
snapshot are received in the wrong order
For example, before the fix, the following occurs:
```
| date | snapshot | | last_ev | last_unev | Snap |
| ---- | -------- | --- | -------- | --------- | ---- |
| 2022 | S2 | | 2022 | | S2 |
| 2020 | S2 | | 2020 | 2022 | S2 |
| 2021 | S2 | | **2021** | **2020** | S2 |
```
as it should be:
```
| date | snapshot | | last_ev | last_unev | Snap |
| ---- | -------- | --- | -------- | --------- | ---- |
| 2022 | S2 | | 2022 | | S2 |
| 2020 | S2 | | 2020 | 2022 | S2 |
| 2021 | S2 | | **2020** | **2022** | S2 |
```
Related to T3000