I started getting problems with Avast and Outlook when I installed Avast in April 2019. Avast could not help so I turned to Microsoft. Initialy thay could help by disabling add ins but then it started again. I asked Avast for a refund in JUly 2019 explaining why but this is the reply that I got:=
-All Avast programs can be used 30 days for free as a trial, and additionally we offer a 30 days money back guarantee from the date of purchase.
On this occasion, it appears that you have missed the guaranteed period.
I kept disabling Avast each time to use Outlook but it became problematic and tedious. Also I had no anti-virus. Having paid for a years subscription I reinstalled it and the problems started again in September 2019.
I turned back to Microsoft Support and after trying various things for weeks, they finally asked me to disable Avast until further notice. I have done that and the problems have ceased. I have no intention of using it again. In my view, it is wasted money and a problematic piece of software, if you are using Windows 10.