Thanks for the answers.
I solved this "memory" issue by:
- switched memory mode to local from distributed;
- switched off SMT in AMD Ryzen Master;
- installing 4x8Gbyte RAM instead of 1x16GB;
- using 8 threads per encode (4 encodes are being run in parallel to reach 100% processor utilization and ~60% level of memory);
- using 1 frame thread per encode with preset slower;
- this way my 1950X System is working stable while encoding time is quite acceptable until I my new PC arrives.