Hello,
Well I solved my 2 (unrelated) problems by myself, even if the support avast never interested in it (by 3 tickets sent or here by avast team).
I just felt like I paid my subscription for 10 years to be considered a free user

So,
- for Web shield down:
due to a missing version of Net Framework (3.0 SP2) , I have only 1 , 2.0 and 3.5.
Informations from the web are true when it says new Net Frameworks releases not necessarily updates older.

What's new before 2218 avast versions , that avast never said me and Which can prevent StreamFilter to run : using Kernel Mode Driver Frameworks service (Wdf01000) this one only set with 3.0 SP2 and seen on my other winxp pc.
Of course MS doesn't want I install it as far as I have subsequent version

I have to remove all Net Framework and restart to the begening.
When Kernel Mode Driver Frameworks appears again in my manager (Hidden peripherals) , avast works again

- for
Invalid or corrupt license event:
It is a question of rights conferred , even if I don't know why - I'am an administrator user who has all right - avast doesn't let me use "aswChLic.exe" totally , more , without notifying me clearly.
nb:on others pc , I have this right.
also strange : why do I haven't problems to set licence on this same pc with old (2218) avast version ?
However , run administrator session at win logon , set licence file on it (OK) , back to my own session and all right

Related:now in my.avast.com , 3 pc use the same expiration Timestamp => 19/10/2018
8:06
before the rebellious pc displayed 19/10/2018
10:06 and 2 others 19/10/2018
8:06
before only the rebellious pc was displayed in use on the licence , now neither about related licence , even if all right in 3 UI.