Hi folks,
try to search within the group but didn’t find anything 
FIrst, in DT3beta it is not possible to multiselect folders in the sidebar (either by CMD or SHIFT).
In the splitted window it is possible to multiselect files.
Second, in DT3 I have to manually to open the library I work with. It didn’t automatically opens it when starting.
Last but not least, in the system.log I found many entrys like this:
May 8 08:15:05 god DEVONthink 3[87844]: DEPRECATED USE in libdispatch client: dispatch source activated with no event handler set; set a breakpoint on _dispatch_bug_deprecated to debug
May 8 08:15:06 god com.apple.xpc.launchd[1] (com.apple.xpc.launchd.domain.user.505): Service “com.devon-technologies.think3.28380” tried to register for endpoint “DevonThinkPro” already registered by owner: com.devon-technologies.thinkpro2.28244
May 8 08:17:34 god DEVONthink 3[87844]: assertion failed: 18E226: libxpc.dylib + 91033 [49138829-09C8-355C-B558-97E070B84EC5]: 0x89
May 8 08:17:34 god com.apple.xpc.launchd[1] (com.adobe.accmac.ACCFinderSync.66E5EAA5-BC43-4E0B-8D97-81651D8FE351[87922]): Caller wanted oneshot behavior for pre-existing instance: caller = DEVONthink 3
May 8 08:17:46 god DEVONthink 3[87844]: objc[87844]: Class FIFinderSyncExtensionHost is implemented in both /System/Library/PrivateFrameworks/FinderKit.framework/Versions/A/FinderKit (0x7fffa384e3c8) and /System/Library/PrivateFrameworks/FileProvider.framework/OverrideBundles/FinderSyncCollaborationFileProviderOverride.bundle/Contents/MacOS/FinderSyncCollaborationFileProviderOverride (0x10b1d7f50). One of the two will be used. Which one is undefined.
May 8 08:18:24 god DEVONthink 3[87953]: DEPRECATED USE in libdispatch client: dispatch source activated with no event handler set; set a breakpoint on _dispatch_bug_deprecated to debug
May 8 08:22:18 god DEVONthink Pro[88062]: DEPRECATED USE in libdispatch client: dispatch source activated with no event handler set; set a breakpoint on _dispatch_bug_deprecated to debug
HTH
Kind regards