Error on adding an arbiter

Adding 5th node getting an error

"Our replica set configuration is invalid or does not include us

Presently all 4 nodes are healthy.

node arb1 arb2
rs1 m1,m2,m2 a1

when I try to add a2 both the arbiters will go unhealhty immediately whereas my arbiter is healhty on itself but not healthy in replica set.

node arb1 arb2
rs1 m1,m2,m2 a1 a2

Error for arbiter in replica set –

a1 – "lastHeartbeatMessage" : "Our replica set configuration is invalid or does not include us"

a2 – "lastHeartbeatMessage" : "Couldn't get a connection within the time limit"

where,

m- data nodes

a- arbiters