Thank you for the comprehensive information, it's very helpful. I see multiple nodes with the same node ID, R8nMMFC3Tq-LDEp4A6lr6w:
{n1-7}{R8nMMFC3Tq-LDEp4A6lr6w}{oufKSehNSU6EwG3M9o9yHw}{10.88.88.231}{10.88.88.231:9300}{xpack.installed=true}
{n2-7}{R8nMMFC3Tq-LDEp4A6lr6w}{3OH8MG9HTv66XE7XxceX3A}{10.88.88.232}{10.88.88.232:9300}{xpack.installed=true}
{n3-7}{R8nMMFC3Tq-LDEp4A6lr6w}{_Bu9AgMKQWCxfLu4oBtrAw}{10.88.88.233}{10.88.88.233:9300}{xpack.installed=true}
This means you've cloned the data paths between these nodes, which you shouldn't do. Instead, start all the nodes with empty data paths and they will form a cluster together.