a) Had about 15 modules being reported as invalid - had to re-download/install. Could not do it via GUI (errors in reload process), had to do it via command line (fwconsole ma)
b) Under 10.13, I had a hybrid pjsip/chan_sip setup (trunks on chan_sip, extensions on pjsip). The upgrade switched me to a chan_sip only setup. Had to go into advanced settings and turn back on pjsip driver.
c) Trunks under chan_sip refused to accept incoming calls. Details here: Incoming calls to SIP Trunk not working after 10.13.66.22 -> SNG7 upgrade
d) Upgrade changed the centos rp_filter config. This messed up my somewhat rare dual NIC configuration. Had to fix by following these directions: http://jensd.be/468/linux/two-network-cards-rp_filter (short explanation: I need two NICs on the same subnet, with different IP addresses.)