You have extensions 1255, 1147, 111 and 3603 all registered from 22.214.171.124:1024, apparently a residential cable modem. Is this a gateway from Spectrum? Is there a separate router/firewall?
Most likely, the trouble is either a SIP ALG (disable it if possible, otherwise using nonstandard ports at both ends may help), or a short UDP timeout in the router (increase it if possible, otherwise shorter registration expiry or keep-alive may help).
Possibly related, why did you “replace” the PBX? If the old one wasn’t working properly, what attempts did you make to troubleshoot and fix the problem? If it was running fine, what were you trying to accomplish?
Probably unrelated, why the apparently random extension numbers on a small system? Why chan_sip? Why did you change the chan_sip port to 5060?