Only indexer 4 appears to be receiving data. Outputs.conf below.
[tcpout]
defaultGroup = default-autolb-group
[tcpout:default-autolb-group]
server = shv-ms-splunki1:9997
server = shv-ms-splunki2:9997
server = shv-ms-splunki3:9997
server = shv-ms-splunki4:9997
The correct form is to put all the destination servers in the same list.
[tcpout:default-autolb-group]
server = shv-ms-splunki1:9997, shv-ms-splunki2:9999, shv-ms-splunki3:9997, shv-ms-splunki4:9997