Trying to trigger life event to switch from HMO to PPO

My employer provides a HMO with Kaiser and a PPO with United Healthcare. I’m currently on the HMO plan and want to switch to the PPO since I maxed out a lifetime specialty treatment. The PPO provides similar coverage for the specialty treatment which I’m very thankful for. Time is a big impact on this treatment so it’s not ideal to wait until my open enrollment in November.

My partners open enrollment is this month. We were thinking he could decline coverage and I can add him on mine to trigger a life event change. When I’m looking in my company’s benefits portal to test how this will work, everything seems fine except when claiming “domestic partner loss of coverage” I only get an option to add him to my HMO plan and I can’t switch to PPO. When I test the life event trigger of “marriage” I get an option to add him and change to PPO.

Does loss of coverage for a domestic partner really not give you the option to switch plans like it does for a marriage? Is this a possible mistake on the portal?