@JoBo_109,
For the issue with indexing not completing the Outlook In App Team has gotten some cases with this symptom lately and they are investigating it. If you have Office Subscription and not submitted an In App ticket please do so by clicking Help, Contact Support. Not everyone has Contact Support but if you do please submit it until it uploads logs and you get a ticket created.
Also, something you could check in case indexing does not have enough computer idle time to complete the index is to give search a higher priority. I cannot find the Microsoft article but this one has the reg key, Force Windows indexing to run faster - Office Watch (office-watch.com). When you set this regkey indexing will be prioritized and your computer may run a little slower otherwise. If you can give this a try please let me know if you see any difference.
INDEXING-FAST.REG
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search\Gathering Manager]
"DisableBackOff"=dword:00000001
Note: This is the default setting:
INDEXING-NORMAL.REG
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search\Gathering Manager]
"DisableBackOff"=dword:00000000