This KB explains the change in auto-negotiation default behaviour in ACX5448 and ACX710

In the previous versions, the auto-negotiation for the LX family of optics on the ACX5448 and ACX710 were enabled by default.

However, now a behavioural change with auto-negotiation for the LX family of optics on the ACX5448 and ACX710 platforms has been incorporated.

Auto-negotiation has been disabled in hardware on all ports of ACX5448 & ACX710 for the LX family of optics via different PR's. This was based on feedback from several customers in the field who were facing different inter-op challenges due to auto-negotiation being enabled. Thus, when using a release having fix of respective PR's, with LX family optics, auto-negotiation will need to be disabled on the peer side interface and the speed and link-mode will need to be manually configured.

Below are the PRs for your reference.

PR1721928 - auto-negotiation disabled for LX family on ACX5448 (from 23.2R2)

PR1828435 - auto-negotiation disabled for LX family on ACX710 (from 24.2R2)