Funnel reports read in master DB instead of slave


We have a cron job running every hour to generate our reports.
When a user create a new goal with an associated funnel, a lot of past reports are generated during the next run of our cron job.

I noticed that there is a huge spike of CPU and read IOPS on the master DB, only when those funnels reports are being processed:

With other reports, the spike would be on slave DB, as expected.

Here is an extract of the logs of the Funnel report generation, matching with the master DB spikes (I removed all the line taking less than 7 seconds):

We use Matomo 4.1.1 and Funnels 4.0.4
Could you please assess why master DB is targeted instead of slave?
Also, i don’t know if it could be related to Funnel reports missing