That looks as if interleaving may have kicked in. It lowers the downstream speed by several Mbps and weirdly increases the maximum rate. Plus adding at least 8ms to the latency.
Have you recently had a new Home Hub or other BT change, or any new/replacement electrical/electronic equipment?
If interleaving is what has happened then the worst thing you can do is repeated restarts/reboots of the router. It can confirm to DLM that it is necessary. If left alone after a while it can often decide to put the line back on fast path.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
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