Where did uncounted heap memory go?

our cluster keeps running in high heap memory, but we can't find where are memories consumed?

here is the output from /_cate/nodes api:

id   version type   jdk    heap.current heap.percent heap.max ram.current ram.percent ram.max fielddata.memory_size query_cache.memory_size request_cache.memory_size segments.memory segments.index_writer_memory segments.version_map_memory segments.fixed_bitset_memory
jSfe 8.9.0   docker 20.0.2        8.8gb           29     30gb     236.4gb          94 251.6gb                48.9mb                  89.3mb                     8.3mb              0b                        1.4mb                        226b                      416.4mb
nckU 8.9.0   docker 20.0.2       20.8gb           69     30gb     124.9gb          99 125.7gb                50.9mb                 105.5mb                     9.8mb              0b                       11.3mb                          0b                      541.5mb
Irxs 8.9.0   docker 20.0.2       14.9gb           49     30gb       112gb          89 125.7gb                47.8mb                 209.1mb                     7.3mb              0b                        1.2mb                          0b                      548.5mb
5qNm 8.9.0   docker 20.0.2       12.5gb           41     30gb      59.6gb          95  62.7gb               102.3mb                   213mb                     8.4mb              0b                        1.1mb                          0b                      650.4mb
PSx4 8.9.0   docker 20.0.2        6.9gb           23     30gb     236.4gb          94 251.6gb               115.4mb                 149.6mb                     8.2mb              0b                       10.7mb                       1.2mb                      785.3mb
lapl 8.9.0   docker 20.0.2       17.4gb           58     30gb     124.9gb          99 125.7gb                63.9mb                 107.3mb                     7.8mb              0b                        1.6mb                       1.5kb                      569.2mb

take the second node as example, 20.8G of 30G heap are used, but summary of the detailed columns of memory used is only 0.8G, where are the uncounted 20GB memory used for?