Altcoin: Send/receive transactions between nodes have high failure rate
The issue has nothing to do with node density. You are getting the error can't broadcast immediately, no witness yet which means that segwit is not active on your coin yet so the spends of segwit outputs will not be broadcast. You must activate segwit by mining enough blocks which signal for Segwit. Having the NODE_WITNESS service bit set does not matter; segwit is a consensus rule and the service bit is meaningless without the consensus rule being active.