The 13500, 13800, 21600, 21700 appliances have a conflict between the LOM and the OS that results in these symptoms.
These appliances have a LOM card that reads the hardware sensors (default SNMP polling interval is 20 seconds). Therefore, Gaia OS and LOM card need to be synchronized. This synchronization mechanism leads to the delay.
The slowness is related to I2C (Inter-Integrated Circuit) bus, CPU and other system resources are not used/slowed.
This is the equivalent in the 21600 and 21700 appliances to the problem described in sk92788 for the 21400 appliance.