[Logs UI] Scrolling up and down to load additional entries doesn't work

[Zacqary]

Kibana version:
7.5

Elasticsearch version:
7.5

Describe the bug:
When scrolling through the log stream and hitting the edge of the loaded data, the Loading additional entries... indicator appears, but then doesn't append additional entries after it's done loading.

Steps to reproduce:

1. Scroll up or down through the logs until you hit the edge of the data
2. Wait for Loading additional entries... to disappear
3. Notice that no additional entries appear
4. Use the log minimap or the toolbar to change the timestamp, and notice that additional entries are actually present earlier or later than the currently loaded data

Expected behavior:
Additional logs are added at the top or bottom of the log stream

Any additional context:
This was discovered on the 8.x Observability shared cluster.

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[Zacqary]

Can confirm this is happening on 7.5

[Zacqary]

Regression was introduced by #44923

Working on a fix