Unable to add to array

I've done this many times before: adding an array to an yet already existing array, but for some reason this isn't working now, and I'm out of clues:

PHP Code:

$influx_server_data = [];
$stats = [
                    'health'        =>  $health,
                    'total_live'    =>  $server->live_total,
//etc etc/
                    'mem_used'      =>  $server->system_stats->memory->used,
                    'mem_total'      =>  $server->system_stats->memory->total,
                ];
                $servers_model->update($live_server->id,$stats);

                //Influx Magic

                // Server influx data
                foreach($stats as $measurement => $value){
                    $influx_server_point = [$measurement, //name of measurement
                        $value, //measurement value
                        ['host' => $live_server->hostname, 'region' => $live_server->region], // optional tags
                        $now
                    ];
                    print_r($influx_server_point);
                    $influx_server_data = $influx_server_data + [$influx_server_point];
                }
                print_r($influx_server_data); 


But for some reason $influx_server_data will only have the array from the first run (health in this case). The first print_r confirms that the foreach works fine and shows the desired array for each run.
I'd be grateful for any insights!