One Aeon HEM v1 might be one too many LOL.. As has been mentioned, power monitoring devices are renowned for sending too many messages. This is often a config issue, but for antiques like that HEM, it's the device too.
Try and reduce Power Monitoring reports to the minimum you need. My favorite example is a Washing Machine... you do not need to a Report for every Watt that gets changed. Typically you'd look at the value when the Washer is idle, then again when it's running and pick a threshold pretty close (20%) to the 2nd higher value. This will tell you that the Washer is On/Running and that's all most people need to know. When the use is well above minimum, it's running, when it's well below minimum, it's stopped. For that use case, there is no need for additional messages. People will often set a small increment and a small time interval.... usually because that's the factory default for those types of device. Most people will want to turn off the timed/periodic report... or at least make it extraordinarily long.
It's not that power monitoring messages are bad, it's the quantity of them if the defaults are accepted. Hundreds of Contact open/close messages will cause the same congestion... it's just harder to achieve.
Roughly speaking... look at your logs... let it run for 5 mins and count the number of events, divide into 300 (5 mins) and your result should be X seconds per event
My 4 hubs are running at about 12 seconds per event at the low end and about 3 seconds per event on the burdened hub, average and I have roughly 65 devices per hub.
As you can see, burstiness isn't factored in, which is exactly what power monitoring does:
dev:212 2021-05-04 12:47:07.059 pm info LaundryRoomWasher power is 0.000 W
dev:212 2021-05-04 12:47:06.966 pm info LaundryRoomWasher energy is 4.138 kWh
dev:212 2021-05-04 12:47:06.962 pm info LaundryRoomWasher energyDuration is 37.1 Days
dev:212 2021-05-04 12:47:06.893 pm info LaundryRoomWasher current is 0.000 A
dev:212 2021-05-04 12:47:06.782 pm info LaundryRoomWasher voltage is 123.879
5 messages, pretty tightly packed. 20 of those in one house would eat a lot of Mesh time, especially if those messages are a the slowest speed of 9.6k/sec.
There are also Runtime Stats to assist with these calculations too. I'm just too used to the days before the wonderful stats.