So, I got home last night to discover my pool level below the skimmers (after several days of rain).
My first suspicion was the spider gasket but after removal, inspection and re-installing, discovered the flexible pipe had blown off the booster pump outlet at the quick-connect. It was late now (and dark), so I just pushed it back on, disabled the cleaner timer and will re-visit this evening.
This got me thinking... Why use flexible PVC pipe at all? everything else uses rigid PVC so why not the booster pump? The quick-connect and flex pipe seem like a bad choice for something under such pressure.