Same thing happened to me. My two sims were married with maximum friendship and max relationship status, but only ever achieved "lovers".
I had to use testingcheats on and then modifyrelationship [Sim1FirstName] [Sim1LastName] [Sim2FirstName] [Sim2LastName] X LTR_Romance_Main and set their romance to 100. After that they achieved soulmates.
Shouldn't have to use cheats but it seems like nothing on the Sims 4 is working as intended.
This happens every now and then with my sim couples too. It’s unbelievable that this has been going on for so many years without the issue being resolved or even properly addressed.
It occasionally occurs when two sims are soulmates and their relationship decays to the point where their relationship status changes to lovers. When you rebuild their romance and/or friendship, their status as lovers gets stuck, even with a maxed out friendship and romance bar. The only way to “fix” it is to cheat the relationship down and then up again(sometimes it takes several attempts). It really shouldn’t be necessary to cheat in order to fix a glitch in the game.
Except that's not it. I've had Sims starting a romance for the first time ever who get stuck at Lovers, not Soulmates.
Even using the cheats is a little wonky and doesn't always work, but after finagling a bit I did fix it on my current Sims. Still ridiculous it's even required.
