I got this problem with my two soundbars (Q700C and Q990C), then, after googling a little, I found this seems to be a general firmware issue with a lot of previous models, from entry to top of the line models.
When you connect a video device to one of your soundbar's HDMI port (in my case, an apple tv 4k and a Nvidia Shield 2019 pro), you will lose the feature to output all refresh rates under 50hz for 1080p, this takes a hit in the very common combo 1080p/24hz.
This is what available resolution/hz combos looks like when my nvidia shield is connected directly to my tv (lg c1):
This is when the same nvidia shield is connected to my q990c:
All the options under 50hz are not available anymore for 1080p.
This kind of problems can be fixed by a firmware update and would be greatly appreciated, I've found people desisting of going with this soundbar on communities like avsforums and reddit entirely because of this feature, it is one of those essential features that one just expects it to be there.
I have the same problem with my Nvidia Shield and Q990C soundbar, and in the end I had to connect the Shield to the TV via eARC and lose DTS audio codec playback.
Are they going to fix this at some point?