I had a similar issue with a customer, but it was never fully confirmed whether this was the root cause of our problem. With this customer, these spikes resulted in downtime. Sometimes the active member would just stall for a short time without triggering a failover, affecting all traffic passing the gateway, other times it would failover but then the standby member would stall for a short time causing the same issue with traffic passing the gateway.
All debugs pointed to software blade updates, causing the spikes when the stalling occurred. But we did receive a hotfix for it, but the issue continued even with the hotfix applied. Sadly, the troubleshooting with TAC took so long that we reverted from R81.20 to R81.10. The problems were with R81.20 - JHF Take 8, Take 10, Take 14 and Take 24, which was the latest JHF before we decided to revert. The issue has yet to happen on R81.10 for this customer.
Difficult to jump to any conclusions based on this. I wouldn't expect R81.10 and R81.20 to behave differently when updating software blades. But there might be other differences within the software, making the installation of this customer have issues when these updates occur when running R81.20 compared to running R81.10. Who knows.
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