Is your custom lot zoned as a beach?
When I play the lifeguard career in Sunlit Tides or other worlds, I change the lot assignments for the beaches already there (as they don’t extend into the ocean and I don’t want my lifeguard Sim to waste their time surveying there). I then place my own beach lot extending into the ocean. Other Sims are pushed to go to my beach while my lifeguard Sim is on duty; everything seems to work fine.
Another way to play the lifeguard career in other worlds without placing custom beaches is to use
this mod, which will allow the career to be played on lots with pools. This can work well in Sunlit Tides as there are already several pool lots. I like to use a mix of pools and beaches when I have an active lifeguard, just for the change in scenery.
