GSM Sync during restart is very slow

The synchronization process of downloading all PUs from the primary GSM takes a very long time (> 1 hour).
Looking at the GSM logs the actual download time per PU is just a few seconds but then there is a significant pause (10 -60 seconds) before the download of the next PU begins.
1. Attached the GSM log
2. Attached 3 thread dumps which contain the following lock:

at org.jini.rio.monitor.ProvisionMonitorImpl$ProvisionMonitorPeer.addPeerOpString(ProvisionMonitorImpl.java:4628) locked <0x0000000081913728> (a org.jini.rio.monitor.ProvisionMonitorImpl$ProvisionMonitorPeer)

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    • addPeerOpString() method is syncronised.

The customer use XAP-12.2.1
The grid size is 49 GSAs, ~400 GSCs, 125 PUs