Seems you still use 2 Gb RAM (1 Gb for Java heap), but CPU load seems to be acceptable when testing with one mixer (60% as statistics page http://wcs:8081/?action=stat shows).
We've tried to reproduce the issue on youe server by publishing a stream to mixer from iOS Safari 14.2 and playing mixer output stream in the same Two Way Streaming example, and we can't reproduce.
So we recommend you to try to reproduce the issue in Two Way Streaming example on iOS device, may be without mixer. If the issue is reproduced, it may be device channel issue. In this case, the following server setting may help