After W10 latest update in MAY 2019 Behavior Shield is turned off on startup

[rocksteady]

My Win10 pc originally had Win8 and then Win8.1. I have few problems, so yours should not be to blame.
Some strange things happen after Win10 updates, particularly the major Win10 feature updates. When that coincides with an Avast version update then that can be compounded.
I have once had to resolve such an issue by doing a complete uninstall (using avast uninstaller), then dowloading and installing latest avast afresh. Before you do that save your avast settings so you can reapply them to the new version (19.5).
I hope that will ultimately provide you a more stable system.

[bob3160]

Thanks to Bob and Schimdthouse for the reference. I carried out the procedures as per as and after the first bootup  both the W10 Defender scan component and Avast Behaviour Shield became switched off even though during the boot up both showed as OK. Also Avast popped a message up saying 'This is embarrassing we need to restart your antivirus' and 'Loading...... this shouldn't not take long' It took four more power downs and boot ups to clear.  It also added another two minutes to the the startup time but I can live with that.  I also find that W10 updates increase boot up times.  This laptop is now 3 and a half years old and was updated to W10 from W8.1 so perhaps like its 83 years old owner (me) is a bit creaky. My and my wife's W10 desktops in general are ok although my desktop closed down if I attempted to do a scan with last version and the one before that of Avast Free so had to uninstall it. I have not attempted to install the latest version.

This should help: Clean Install of Avast:
https://goo.gl/4Ptzkf
If you need additional help with the Clean Install, watch this:
https://youtu.be/p-h3myRD51A

[nalo89]

I did use the Avastclear function as set by Bob and although the hiccups occurred as in my last reply Avast free is now running perfectly without any further problems on this laptop. In the past I have always updated over the existing version without any problems except for versions 19.4 and 19.5. Then again, previous versions to these two caused no problems as perhaps there were no W10 updates closely aligned to thosed updates.  I may now attempt to install 19.5 on my W10 desktop to see if it takes ok.  Previous Avast Free versions installed ok on the desktop and it was only when the internal HDD died and replaced with a Toshiba HDD that  Avast Free closed down the computer although I cannot pin down the cause of that happening. 

[nalo89]

 "I may now attempt to install 19.5 on my W10 desktop to see if it takes ok.  Previous Avast Free versions installed ok on the desktop and it was only when the internal HDD died and replaced with a Toshiba HDD that  Avast Free closed down the computer although I cannot pin down the cause of that happening." Re the above quote from my last reply. Today I ran Avastclear on the Desktop, installed Avast Free v19.5, Customised the setups and did a Smart Scan with no problems. I then powered down, booted up and carried out another Smart Scan with no problems.