fstrim: /: the discard operation is not supported

[hede <debian452@der-he.de>]

Hi, 

on bullseye fstrim was working fine, but after the upgrade to bookworm fstrim stops working. 
Setup is: ext4 on LUKS on LVM on SSD

# lsblk --discard
NAME                    DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda                            0      512B       2G         0
├─sda1                         0      512B       2G         0
└─sda2                         0      512B       2G         0
  └─sda2_crypt                 0        0B       0B         0
    ├─volgrp-swap              0        0B       0B         0
    ├─volgrp-root              0        0B       0B         0
    └─volgrp-home              0        0B       0B         0

Trimming the EFI partition (sda1) is fine, but trying to trim root or home results in:
fstrim: /: the discard operation is not supported

The command...
#dmsetup table /dev/mapper/sda2_crypt --showkeys
...doesn't show any allow-discard and because of this and the lsblk output I think it's cryptsetup/luks which is not working correctly here. 

But the crypttab includes:
sda2_crypt UUID=[UUIDishere] none luks,discard

I've added "issue_discards = 1" to /etc/lvm/lvm.conf without success - and btw. that wasn't needed before the upgrade. 

Any hints what to test or where to search for a solution?

regards 
hede