Initial sync freezes

We caught a problem during initial sync, at first the data is actively flowing, this can also be seen from the graphs:
The occupied disk space is growing, there is a load on the CPU, etc., but at a certain moment the overflow seems to freeze, the graph in place reaches a plateau, the load on the CPU drops, and in the end it hangs for quite a long time until we get out of the oplog window.
We seem to be going through resources…
Please tell me where we can dig to understand what we are up against?
It is necessary to synk 3TB, 4.4 community, on similar disks previously 1 TB was transferred in 2 hours