Outlook roaming signatures

We recently upgraded the office to 365 in the organization, and moved the users' mailboxes to the cloud.
We are trying to enable the roaming signatures feature, but for some reason we are experiencing incompatibility in the signature roaming behavior.
For some users, when sighning in to different desktops, the signatures are transferred automatically, and for some they are not. For some users, not all signatures are mobile (even though they are all set under the account and not under a local device).
I would love to know what exactly needs to be configured both on the server side and on the client side, so that the signatures will migrate uniformly for all users on all machins.

We work with Microsoft® Outlook® for Microsoft 365 MSO (version 2405 Build 16.0.17628.20006) in 64-bit version.
Thanks,

Tamar