Unknown NullPointerException caused connection termination

[fang10]

We have seen our system occasionally terminated the outbound connection for some traffic. It seems happen when the system is waiting for the payload from backend service.

In the system log, we see NPE errors thrown from Zuul. See stack trace below for details.
LOG_1

message: Error with filter: -, path: /xxxx, method: POST
stack_trace: 
j.l.NullPointerException: parameter 'runningFilterIndex' cannot be null
	at c.n.s.i.Preconditions.checkNotNull(Preconditions.java:35)
	at c.n.z.n.f.BaseZuulFilterRunner.getRunningFilterIndex(BaseZuulFilterRunner.java:105)
	at c.n.z.n.f.ZuulFilterChainRunner.filter(ZuulFilterChainRunner.java:108)
	at c.n.z.f.e.ProxyEndpoint.filterResponseChunk(ProxyEndpoint.java:340)
	at c.n.z.f.e.ProxyEndpoint.lambda$invokeNext$1(ProxyEndpoint.java:326)
	at c.n.z.n.s.MethodBinding.bind(MethodBinding.java:42)
	at c.n.z.f.e.ProxyEndpoint.invokeNext(ProxyEndpoint.java:326)
	at c.n.z.n.s.OriginResponseReceiver.channelRead(OriginResponseReceiver.java:80)
	at i.n.c.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at i.n.c.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	... 51 frames truncated

LOG_2

message: ClientResponseWriter caught exception in client connection pipeline: Channel: [id: 0x2f0b1a18, L:/x.x.x.x:8080 - R:/y.y.y.y:41728], active=true, open=true, registered=true, writable=true, id=2f0b1a18, 
Passport: CurrentPassport {start_ms=1661474271456, 
[
  +0=IN_REQ_HEADERS_RECEIVED, 
  +142857=FILTERS_INBOUND_START, 
  +746476=IN_REQ_LAST_CONTENT_RECEIVED, 
  +7517278=FILTERS_INBOUND_END, 
  +7593714=ORIGIN_CONN_ACQUIRE_START, 
  +7594596=ORIGIN_CONN_ACQUIRE_END, 
  +7629669=OUT_REQ_HEADERS_SENDING, 
  +7679089=OUT_REQ_LAST_CONTENT_SENDING, 
  +7740466=OUT_REQ_HEADERS_SENT, 
  +7743783=OUT_REQ_LAST_CONTENT_SENT, 
  +225603027=IN_RESP_HEADERS_RECEIVED, 
  +225634814=FILTERS_OUTBOUND_START, 
  +225780680=FILTERS_OUTBOUND_END, 
  +225800353=OUT_RESP_HEADERS_SENDING, 
  +225841816=OUT_RESP_HEADERS_SENT, 
  +227994402=NOW
]}

stack_trace:
j.l.NullPointerException: parameter 'runningFilterIndex' cannot be null
	at c.n.s.i.Preconditions.checkNotNull(Preconditions.java:35)
	at c.n.z.n.f.BaseZuulFilterRunner.getRunningFilterIndex(BaseZuulFilterRunner.java:105)
	at c.n.z.n.f.ZuulFilterChainRunner.filter(ZuulFilterChainRunner.java:108)
	at c.n.z.f.e.ProxyEndpoint.filterResponseChunk(ProxyEndpoint.java:340)
	at c.n.z.f.e.ProxyEndpoint.lambda$invokeNext$1(ProxyEndpoint.java:326)
	at c.n.z.n.s.MethodBinding.bind(MethodBinding.java:42)
	at c.n.z.f.e.ProxyEndpoint.invokeNext(ProxyEndpoint.java:326)
	at c.n.z.n.s.OriginResponseReceiver.channelRead(OriginResponseReceiver.java:80)
	at i.n.c.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at i.n.c.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	... 53 frames truncated

LOG_3

message: ClientResponseWriter caught exception in client connection pipeline: Channel: [id: 0xaf8c22ac, L:/x.x.x.x:8080 - R:/y.y.y.y:50388], active=true, open=true, registered=true, writable=true, id=af8c22ac, 
Passport: CurrentPassport {start_ms=1661474239671, 
[
  +0=IN_REQ_HEADERS_RECEIVED, 
  +140498=FILTERS_INBOUND_START, 
  +936973=IN_REQ_LAST_CONTENT_RECEIVED, 
  +6553469=FILTERS_INBOUND_END, 
  +6633562=ORIGIN_CONN_ACQUIRE_START, 
  +6635050=ORIGIN_CONN_ACQUIRE_END, 
  +6684741=OUT_REQ_HEADERS_SENDING, 
  +6726169=OUT_REQ_LAST_CONTENT_SENDING, 
  +6821852=OUT_REQ_HEADERS_SENT, 
  +6826904=OUT_REQ_LAST_CONTENT_SENT, 
  +276210601=IN_RESP_HEADERS_RECEIVED, 
  +276262474=FILTERS_OUTBOUND_START, 
  +276452723=FILTERS_OUTBOUND_END, 
  +276474704=OUT_RESP_HEADERS_SENDING, 
  +276530773=OUT_RESP_HEADERS_SENT, 
  +276540177=IN_RESP_LAST_CONTENT_RECEIVED, 
  +277482075=NOW
]}

stack_trace:
j.l.NullPointerException: channel handler context
	at c.g.c.b.Preconditions.checkNotNull(Preconditions.java:907)
	at c.n.z.n.f.BaseZuulFilterRunner.getChannelHandlerContext(BaseZuulFilterRunner.java:89)
	at c.n.z.n.f.BaseZuulFilterRunner.handleException(BaseZuulFilterRunner.java:380)
	at c.n.z.n.f.ZuulFilterChainRunner.filter(ZuulFilterChainRunner.java:161)
	at c.n.z.f.e.ProxyEndpoint.filterResponseChunk(ProxyEndpoint.java:340)
	at c.n.z.f.e.ProxyEndpoint.lambda$invokeNext$1(ProxyEndpoint.java:326)
	at c.n.z.n.s.MethodBinding.bind(MethodBinding.java:42)
	at c.n.z.f.e.ProxyEndpoint.invokeNext(ProxyEndpoint.java:326)
	at c.n.z.n.s.OriginResponseReceiver.channelRead(OriginResponseReceiver.java:80)
	at i.n.c.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	... 52 frames truncated

As a temp workaround, we buffer the response payload by overriding the needsBodyBuffered method in an outbound filter.
Any thoughts on why it happened? Could this be a Zuul bug? Would Zuul upgrade to a later version fix it?

Zuul: v2.1.7
netty-codec-http2:4.1.59.Final