The following bugs and issues are known for ksh 93u+m 1.0.0-rc1:

Memory leak when initialising associative array in subshell
https://github.com/ksh93/ksh/issues/94

command substitution botches output of non-waited-for child processes
https://github.com/ksh93/ksh/issues/124

wrong typeset -p output after unsetting multidimensional array elements
https://github.com/ksh93/ksh/issues/148

printf %T date parsing: GNU-style "ago" date spec completely broken
https://github.com/ksh93/ksh/issues/182

typeset -L/-R: string length breaks on multibyte characters
https://github.com/ksh93/ksh/issues/189

Unicode code points in $'...' strings should vary according to the locale
https://github.com/ksh93/ksh/issues/193

Variable expansion corruption in single-line function on 32-bit systems
https://github.com/ksh93/ksh/issues/203

Segfault with very large extended glob patterns
https://github.com/ksh93/ksh/issues/207

process substitution cannot be part of a larger argument
https://github.com/ksh93/ksh/issues/215

Nested compound assignment misparsed in $(...) command substitution
https://github.com/ksh93/ksh/issues/269

Builtins don't handle I/O errors
https://github.com/ksh93/ksh/issues/313

bug in printf when %b and %x$ are used in same format
https://github.com/ksh93/ksh/issues/324

namespaces don't work properly when defined within functions
https://github.com/ksh93/ksh/issues/325

Associative arrays of various types fail to be unset
https://github.com/ksh93/ksh/issues/345

Variable with discipline function in subshell causes memory leak
https://github.com/ksh93/ksh/issues/404

Memory leak(s) when modifying PATH in various contexts
https://github.com/ksh93/ksh/issues/405

Discipline function .unset only called once for array subscripts
https://github.com/ksh93/ksh/issues/419

Function autoload apparently broken on DragonFly BSD
https://github.com/ksh93/ksh/issues/432

confusing behaviour of backreferences with alternation
https://github.com/ksh93/ksh/issues/447

Alias expansion loop not detected in command substitution
https://github.com/ksh93/ksh/issues/458

Make KEYBD trap handling code multibyte-aware
https://github.com/ksh93/ksh/issues/460

$LINENO incorrect after compound assignment
https://github.com/ksh93/ksh/issues/484

Shell quoting within bracket patterns has no effect
https://github.com/ksh93/ksh/issues/488