We regularily have the same problem. Thus we created a script that does all the unregistration of old COM-objects and re-registering a newer version - e.g. efter compiling our ArcObjects-code. This script executes ESRIRegAsm to do the esri-registration:
set EsriRegasm="%CommonProgramFiles%\ArcGIS\bin\ESRIRegAsm.exe"
IF EXIST MyAssembly.DLL %EsriRegasm% /p:desktop /u /s MyAssembly.dll
After re-building our assembly and calling EsriRegAsm again in order to register the new version you should be able to see the entry within the windows-registry as mentioned in your question plus an ECFG-file with the samext same name as your assembly (with extension .ecfg) in C:\Program Files (x86)\Common Files\ArcGIS\Desktop10.6\Configuration\CATID. If the file is not there, ArcMap won´t find your toolbar.
You can also open that file, it´s basically a zip-file containing a config.xml. This file contains the GUIDs of your toolbars and its related tools and commands.
In some cases you may have a file from a previous build also, which has a name similar to {3c7448a8-c8b9-4704-aa14-699ed583132b}_MyAssemmbly.cmds. You should delete those files.