Same issue here, except it hasn't magically fixed itself yet. Here is the output from gdb. Hadn't used gdm since my days of coding MUDs

PS: I'm on the latest Macbook pro.

(gdb) run
Starting program: /Applications/lxdream.app/Contents/MacOS/lxdream
Reading symbols for shared libraries +++++++++++++++......................................................................... done
18:03:02 00000000 WARN Unable to load file 'dcboot.rom': No such file or directory
18:03:02 00000000 WARN Unable to load file 'dcflash.rom': No such file or directory
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries .. done
Reading symbols for shared libraries . done
sh4/sh4trans.c:231: failed assertion `IS_IN_ICACHE(sh4r.pc)'

Program received signal SIGABRT, Aborted.
0x9131ab9e in __kill ()
(gdb) bt
#0 0x9131ab9e in __kill ()
#1 0x9131ab91 in kill$UNIX2003 ()
#2 0x91391ec2 in raise ()
#3 0x913a147f in abort ()
#4 0x0005cebd in __eprintf (string=0x0, expression=0x0, line=0, filename=0x0) at /var/tmp/gcc/gcc-5465~16/src/gcc/libgcc2.c:1838
#5 0x000503d3 in xlat_get_code_by_vma ()
#6 0x00050458 in sh4_translate_run_slice ()
#7 0x00012b2f in sh4_run_slice ()
#8 0x00010a1e in dreamcast_run ()
#9 0x94c3c73e in __NSFirePerformTimer ()
#10 0x9591a9c2 in __CFRunLoopDoObservers ()
#11 0x9591bd1c in CFRunLoopRunSpecific ()
#12 0x9591ccf8 in CFRunLoopRunInMode ()
#13 0x92344da4 in RunCurrentEventLoopInMode ()
#14 0x92344af6 in ReceiveNextEventCommon ()
#15 0x92344a31 in BlockUntilNextEventMatchingListInMode ()
#16 0x95003505 in _DPSNextEvent ()
#17 0x95002db8 in -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] ()
#18 0x94ffbdf3 in -[NSApplication run] ()
#19 0x00056e48 in gui_main_loop ()
#20 0x00007444 in main ()