A few days ago, I downloaded the latest version (at that time) from github.com. In January 1999, the alien mission STR_SENTRY_RETALIATION by STR_SNAKEMAN_SALAMANDRON ended with the base defense, which, judging by the number of SALAMANDRONs,
is not SENTRY retaliation.
Perhaps a line "missionCustomDeploy: STR_BASE_DEFENSE_SENTRY" in the section "- type: STR_SENTRY_SHIP" of the file ufos_XCOMFILES.rul is needed.
The save file is attached.Upd:
Solarius Scorch, thank you! (I remove the attached file, since the problem is solved and the file is not needed)