we have the same problem. I tried to observe the samba logs live on terminal and this line "Bad SMB2" comes up whenever the "destination folder access denied" appears.
Apr 26 10:23:56 MIR-Server webgui: Successful login user root from 192.168.8.178
Apr 26 10:34:04 MIR-Server smbd[369283]: [2025/04/26 10:34:04.768375, 0] ../../libcli/smb/smb2_signing.c:646(smb2_signing_check_pdu)
Apr 26 10:34:04 MIR-Server smbd[369283]: Bad SMB2 (sign_algo_id=2) signature for message
Apr 26 10:34:04 MIR-Server smbd[369283]: [2025/04/26 10:34:04.768441, 0] ../../lib/util/util.c:580(dump_data)
Apr 26 10:34:04 MIR-Server smbd[369283]: [0000] 13 7A 93 FB 1D 0E D9 6E 6D E1 A1 8C 22 98 F3 A6 .z.....n m..."...
Apr 26 10:34:04 MIR-Server smbd[369283]: [2025/04/26 10:34:04.768464, 0] ../../lib/util/util.c:580(dump_data)
Apr 26 10:34:04 MIR-Server smbd[369283]: [0000] 92 A4 B4 7B AD 5A FC 4A C3 49 2F E8 4D 6D E9 9A ...{.Z.J .I/.Mm..
Apr 26 10:36:17 MIR-Server smbd[369283]: [2025/04/26 10:36:17.211892, 0] ../../libcli/smb/smb2_signing.c:646(smb2_signing_check_pdu)
Apr 26 10:36:17 MIR-Server smbd[369283]: Bad SMB2 (sign_algo_id=2) signature for message
Apr 26 10:36:17 MIR-Server smbd[369283]: [2025/04/26 10:36:17.211933, 0] ../../lib/util/util.c:580(dump_data)
Apr 26 10:36:17 MIR-Server smbd[369283]: [0000] 83 15 34 51 EC E3 54 AF 50 A8 C6 05 CA A6 78 1F ..4Q..T. P.....x.
Apr 26 10:36:17 MIR-Server smbd[369283]: [2025/04/26 10:36:17.211953, 0] ../../lib/util/util.c:580(dump_data)
Apr 26 10:36:17 MIR-Server smbd[369283]: [0000] 53 8E 53 63 3D 69 AD F7 6E 0B 0D 0A 1C C4 10 3E S.Sc=i.. n......>
Apr 26 10:38:27 MIR-Server smbd[369283]: [2025/04/26 10:38:27.915962, 0] ../../libcli/smb/smb2_signing.c:646(smb2_signing_check_pdu)
Apr 26 10:38:27 MIR-Server smbd[369283]: Bad SMB2 (sign_algo_id=2) signature for message