Thanks @Chris . But the problem wont be solved if we remove the ARBITER. Also we are not using readConcern majority. I changed the server defaultWriteConcern to w:1.
Coming to the mongo workaround of setting priority and votes=0 if the secondary member is lagging or unavailable doesnt look like a native solution. Also it violates the mongo fault tolerance claim. out of 5 member replica , 2 members can go down and mongo should run healthy. But after this 5.0, its no longer the case.