Electrical wiring problem in panel when using 220 volt log splitter
With multiple dead outlets on each side you have lost a leg as I said so there will not be power on the odd or even breakers under load with no load there may still be a conductive path creating some voltage at an outlet but no ability to support a load. When you turn on a 240 device the power is being delivered to the the bad leg through this device or log splitter. All the odd breakers are connected to 1 leg and all the even are connected to the other leg for single pole. The supply to the panel from the main has a problem. It could be the breaker in the service panel that feeds the sub or 1 wire connecting the breaker to the panel or someplace in between so all the breakers on the odd or even side (L1 or L2 will be dead). Check at the service panel for 120 to neutral on each then 240 across the 2 then check the sub the same way. If you see 240 at the service connection but not at the sub and the connections look good the feeder wire has a break someplace in between.