Not that "SwapTotal:" and "SwapFree:" are reported as 0 kB.
When running 'show tech-support -bundle', the free swap space is reported as zero for the APMs.
There is a swap space allocated on the CPM level but that has a directly connected disk drive. When running 'show tech-support -bundle', free swap may may appear to have dropped to zero temporarily. However, the swap space reported is for the VAPs on the APMs, where there is no swap space pre-allocated
Seeing 0kB swap values is normal on the VAPs, it does not represent an issue. VAP members have no swap space allocated as this would enable potential swapping via the control plane through NFS which would considerably impact performance.
what causes it to go to 0kb? > Swap space is not configured on the APMs by design.
Does it ever come back to a non-zero value? > No, swap space is not pre-configured at all on the APMs.