I have a table in Bigtable named "orders" with one column family "order-family". It returns this configuration Column Family: order-family GC Rule: {"gcRule":{"maxAge":"86400s"}}.
I can insert data into the "orders" table, but after 30 minutes the data is automatically removed, but I don't know why.
Your data is being garbage collected after it reaches an age of 86400s as you stated in your question. That means your data will be deleted after that amount of time. To fix this, update your column family to not have a garbage collection rule, or don't create it with one in the first place.
You might want to read up more on garbage collection before using it.