Safari 12.0 introduced a bug in H.264 encoding which, when combined with OpenH264 as the decoder on the remote end, causes video "flickering" or "freezing". There is no issue when Chrome or Firefox is the remote peer because they use a decoder which works around the problematic data encoded by Safari. Cisco's current version of the OpenH264 decoder does not support the required work around, and so issues decoding the erroneous data cause excessive PLIs.
Safari 12.1 introduces VP8 support, so we've provided a work-around to Safari video quality issues in LiveSwitch 1.3.2 by ensuring that VP8 is negotiated through modifying the SDP offer/answer. Please note that Safari 12.0 does not include support for the VP8 codec, so for users using the Safari 12 series the simplest work-around is to upgrade to the latest version of LiveSwitch and Safari.