Error in loading .rds sim files

I have been running some simulations that are quite computationally lengthy (i.e. take >30min). The final sim objects have been working fine, with full functionality, including plotting. To store the simulations I used the code e.g. sim18$save("sim18.rds"). However, when loading the sim object with the code sim18<-PM_sim$new("sim18.rds"), the loaded sim returns errors when e.g. trying to plot from it. So sim18$plot() returns the following when using the saved file: > Error in simout$obs[!is.na(simout$obs$out), ] : > incorrect number of dimensions However, re-running the sim and plotting from the freshly created sim file works with the same command. I can obviously work around this, but raising in case this is a bug. If it is something I am doing incorrectly, advice would be appreciated.