xkb: Why is the compose key set to NoSymbol after a system update (OpenSuSE 15.2 → 15.3)?

After upgrading my OpenSuSE Leap from 15.2 to 15.3, I found out that the Compose key (keycode: 135) was no longer working. In fact, xev no longer recognised it as Multi_key, but as NoSymbol:

KeyPress event, serial 40, synthetic NO, window 0x7800001,
    root 0x561, subw 0x0, time 8470151, (923,367), root:(923,396),
    state 0x10, keycode 135 (keysym 0x0, NoSymbol), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

NB: The key is really labeled Compose, as it's part of a Sun Type 7 keyboard. In the $XKB/keycodes/evdev file, I've got these two lines of code (of which the second one has been disabled by me, as it's for regular PC keyboards with Menu keys):

= 135;
// alias  = ;

The $XKB/symbols/compose file has been upgraded with the following block:

partial modifier_keys
xkb_symbols "comp" {
    key   { type[Group1]="TWO_LEVEL", [ Multi_key, Multi_key ] };
};

The current setxkbmap config looks as follows:

╭─jacek@epica ~  
╰─➤  setxkbmap -print -verbose 10                                         127 ↵
Setting verbose level to 10
locale is C
Trying to load rules file ./rules/evdev...
Trying to load rules file /usr/share/X11/xkb/rules/evdev...
Success.
Applied rules from evdev:
rules:      evdev
model:      pc105
layout:     de
variant:    pl
options:    compose:comp,terminate:ctrl_alt_bksp,altwin:meta_win,lv3:ralt_switch
Trying to build keymap using the following components:
keycodes:   evdev+aliases(qwertz)
types:      complete
compat:     complete
symbols:    pc+de(pl)+inet(evdev)+terminate(ctrl_alt_bksp)+altwin(meta_win)+level3(ralt_switch)+terminate(ctrl_alt_bksp)
geometry:   pc(pc105)
xkb_keymap {
        xkb_keycodes  { include "evdev+aliases(qwertz)" };
        xkb_types     { include "complete"      };
        xkb_compat    { include "complete"      };
        xkb_symbols   { include "pc+de(pl)+inet(evdev)+terminate(ctrl_alt_bksp)+altwin(meta_win)+level3(ralt_switch)+terminate(ctrl_alt_bksp)"  };
        xkb_geometry  { include "pc(pc105)"     };
};

I can see the compose:comp option very clearly. So: What's wrong here?