It seems to me at one time I was able to just click the check box "Enable Profile Corrections" and LR would automatically detect the lens I used and apply it.
Now it wants me to scroll through the list to the bracnd name--then it applies it.
It detects it from the embedded EXIF usually. Not all cameras write the EXIF as required. I've at least 2 descriptors for my 24-70L for example depending on which camera wrote them. So it may know that it's a 24-70, but not which on until you start selecting.
When auto detection fails, you can fix a particular profile as your new default, against the lens data found for the active image. It's an option in the lens profile selection drop-down menu. LR will use that chosen profile automatically from now on, whenever other images are encountered which show the same lens data. The profile selection will then read "default" rather than "manual" / custom / whatever.
One common problem happens where people have switched from using JPG to Raw, or vice versa. Profile support is independent for these two cases, even for the same lens mounted on the same camera format. Each profile file states whether it is specific to Raw, or to non-Raw. So it may appear that a lens profile which used to work has now disappeared, when the reality is that a different list is now being presented to suit this current image's format.
Many profiles are Raw-only. These can be "cheated" so as to also work for JPG, by altering a differently named copy using a text editor - changing the line which says this profile is for Raw, from "True" to "False". So long as there's been no in-camera correction of JPG, it works OK; though I guess the optimum would be a profile that had been originally generated from camera JPGs in the proper manner.
When you select a picture taken with a particular lens, and manually go through the list of brand names and lenses, is the profile you want there?
When you enable lens profile, does the selection box below that state Default, Auto - or Custom?
If set to Default, have you tried to lock in the profile selection you want, as your new automatic default for this particular lens, by selecting it in the list, and then choosing Save New Lens Profile Defaults in the same selection box?