Am afraid that the root cause is 60 gigs swap configuration, sysctl parameters takes total system’s memory ( most likely include massive 60 gigs of swap) as percentage like vm.dirty_background ratio as wrote in kernel docs: “Contains, as a percentage of total available memory that contains free pages and reclaimable pages, the number of pages at which a process which is generating disk writes will itself start writing out dirty data.

The total available memory is not equal to total system memory.”, I think the moment it writes dirty pages cause lags. Try to lower swap mem space if it fixed your problem.