Major Description
After PHOENIX-4214, we stop inbound writes after a split is requested, to avoid split starvation.
However, it seems there can be edge cases, depending on the split policy, where a split is not retried. For example, IncreasingToUpperBoundSplitPolicy relies on the count of regions, and balancer movement of regions at t1 could make it such that the SplitPolicy triggers at t0 but not t2.
However, after the first split request, in UngroupedAggregateRegionObserver the flag to block inbound writes is flipped indefinitely.