Glyphs crashes when displaying multiple substitution with classes

Glyphs
1

By adding a multiple class substitution to my rclt feature (as in the documentation, here), Glyphs crashes systematically when it tries to display it in the preview. The same line of code seems to work on the same file when imported into Fontlab.

sub @A @A' @A by B C;

I don’t really know if the line of code is supposed to work as I intend, but the fact that Glyphs crashes for this is a real problem.
I use the latest version.

Thanks in advance,
Clara

2

What version of Glyphs do you have?

When it crashes, There should be a dialog with a “Show Details” button in the lower left. Can you click that button and post the first few pager from the details text (copy paste it here).

3

I use Glyphs 3.3.1.
When I initially had the problem there used to be a dialog but I can’t reproduce it (now it just crashes); but I still have a crash report from the console, I hope it can helps.

Crash report 
Date/Time:        2025-06-13 09:21:15.610 +0200
End time:         2025-06-13 15:17:48.413 +0200
OS Version:       macOS 14.5 (Build 23F79)
Architecture:     arm64e
Report Version:   49
Incident Identifier: 876879A3-42A5-4FCB-B5FC-09CB4F225C41

Data Source:      Microstackshots
Shared Cache:     3406AD1B-2469-30EB-9863-5DCE861E6DEA slid base address 0x19688c000, slide 0x1688c000

Command:          Glyphs 3
Path:             /Applications/Glyphs 3.app/Contents/MacOS/Glyphs 3
Identifier:       com.GeorgSeifert.Glyphs3
Version:          3.3.1 (3343)
Team ID:          X2L8375ZQ7
Is First Party:   No
Beta Identifier:  CA62A04B-103E-57D2-9D5A-7E82069FBCF3
Resource Coalition ID: 633
Architecture:     arm64
Parent:           UNKNOWN [1]
PID:              618

Event:            disk writes
Action taken:     none
Writes:           2147.49 MB of file backed memory dirtied over 21393 seconds (100.38 KB per second average), exceeding limit of 24.86 KB per second over 86400 seconds
Writes limit:     2147.48 MB
Limit duration:   86400s
Writes caused:    2147.49 MB
Writes duration:  21393s
Duration:         21392.80s
Duration Sampled: 21374.71s
Steps:            166 (10.49 MB/step)

Hardware model:   iMac21,2
Active cpus:      8
HW page size:     16384
VM page size:     16384

After the crash, it becomes impossible to open Glyphs, even from another file, without holding shift. When I finally manage to reopen the file (which can sometimes take a large number of attempts and restarting my OS), deleting the line of code from my features seems to prevent from any further crashes.