HTTP2 specification clearly states that:
Values above the maximum flow-control window size of (2^31)-1 MUST be treated as a connection error of type
FLOW_CONTROL_ERROR.
What is the rationale for this hard limit? What does the limit accomplish? What potential problems is the specification trying to solve by this?
Most likely a concession to languages (like Java) that have signed and unsigned bits so only have 31 bits to play with for integers. Similar to this: Why is the stream identifier 31 bit in HTTP/2 and why is it preceded with a reserved bit?