Why reading data on grafana takes time after restart

So whenever we restart influxdb, we notice that it takes quite a while for grafana to reconnect/read data from influxdb.(up to ~10m)

However, when it comes to writing data and accessing /health endpoint the DB is available within ~2-3 mins.

Why does the DB take a longer time to serve reads after the DB service/process is restarted?

Is it related to WAL flushing, but why does that affect read?