This error appears if Magento is trying to store more data in the Redis cache then possible.
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Verifying Memory Usage of Your Redis Instance
You can see the memory values by using the redis-cli:
redis-cli info memory # Memory used_memory:894168 used_memory_human:873.21K used_memory_rss:9293824 used_memory_peak:1181776 used_memory_peak_human:1.13M used_memory_lua:33792 mem_fragmentation_ratio:10.39 mem_allocator:jemalloc-3.6.0
You can try to fix this using compression on the Redis data, but most of the time this will only temporary ban out the problem. After a while, when the Redis cache is completely filled up again, the errors will re-appear.
If you store both the Magento caches (FPC and cache) and the sessions in Redis, it could help moving the sessions from memory to files or the database, but this can cause increase in load times.
Another fix could be removing your staging environment from the Hypernode, leaving the staging memory for the production website. (Don’t forget to clear it’s caches too!)
To solve this issue there is only one real fix: Upgrade to a bigger node that has more memory.