5.5fc1 seems to have a memory problem, at least with largish settings files, and on my LC 475 (7.5.5 w/OpenTransport). Logging on to my BBS over a TCP connection, using a 3253K experimental settings file, the available memory drops down to less than 20K very quickly. Folders will refuse to open sometimes, and windows will lose their graphics, and sounds, sometimes. I crashed once with a 25 memory error (log attached).
Using the same settings file, 5.5b22 runs fine, leaving around 220K free, opening everything etc. Would you like to see that file?