Web Site with page using Javascript are very Slow

Hi

First : Sorry for my poor English

In My site we use many Symantec endpoint version 12.1.x on W7 64 bits.

and all version have the same Issue Only on IE9 and IE11 (Work perfectly on Firefow or Chrome)

A web page using Javascript is very slow. If i Uncheck option "Enabled Intrusion Prevention" the web site display quicky.

This issue came since a few days (Probably 2 week)

- I runned Symdiag : no error

- I runned liveupdate, no issue, virus def are uptodate, no error in a logs

- I installed manually full virus def 20171017-016-v5i64.exe : no issue, virus def are uptodate, no error in a logs

Have you an idea.