I have done all this and the issue is remaining

I can add that when I edit the post the video appear but disappear when i save the post

What I have done with deleting all cache at different times

In wprocket in the Never Cache URL(s) list.

wp-admin/options-general.php?page=wprocket#advanced_cache

I add like asked

/my-forum-name/derniers-messages/(.*)
/my-forum-name/(.*)

and in wp-admin/options-general.php?page=wprocket#file_optimization

my list of is 

/app/js/api.min.js
feedbackcompany.com/includes/widgets/feedback-company-widget.min.js
snap.licdn.com/li.lms-analytics/insight.min.js
static.ads-twitter.com/uwt.js
platform.twitter.com/widgets.js
/sdk.js
static.leadpages.net/leadbars/current/embed.js
translate.google.com/translate_a/element.js
xfbml.customerchat.js
smartsuppchat.com/loader.js
pinit.js
/gtm.js
fbevents.js
google-analytics.com/analytics.js
ft.sdk.min.js
apps.elfsight.com/p/platform.js
livechatinc.com/tracking.js
pixel-caffeine/build/frontend.js
wp-content/plugins/visitors-online/js/script.js
wp-content/plugins/visitors-online/bws_menu/js/shortcode-button.js
wp-content/plugins/visitors-online/bws_menu/js/c_o_o_k_i_e.js
frontend.js
ajax.js
widgets.js

So I added with success

frontend.js
ajax.js
widgets.js

But I cannot add 

wpforo

tinymce

Because these 2 lines disappear when i save

Thank your for your answer,

for this post this is good when I change

but i think there is an another general problem with others video for example like 

https://www.vivrenu.com/forum-du-naturisme/postid/2204970/

with the source code 

<p>[Elite_video_player id="61343"]</p>
<p>ou</p>
<p><video controls="controls" width="100%"><source src="https://download.vivrenu.com/1974_ina_agde_congres_naturistes.mp4" type="video/mp4" /></video></p>

and the short code for elite video player also dont work

And in my test website everything is okay with the source code including height="auto" and I dont know why and which difference there is

see at https://test.vivrenu.com/forum-du-naturisme/postid/2204970/

elite video player dont work with wpforo 1.99 but is okay with wpforo 1.96

<p>[Elite_video_player id="61343"]</p>
<p>ou</p>
<p><video controls="controls" width="100%" height="auto"><source src="https://download.vivrenu.com/1974_ina_agde_congres_naturistes.mp4" type="video/mp4" /></video></p>

This test url will be remove soon

Posted by: @gilbau

but i think there is an another general problem with others video for example like 

https://www.vivrenu.com/forum-du-naturisme/postid/2204970/

with the source code 

The same was here, the height was 0px.

Posted by: @gilbau

and the short code for elite video player also dont work

If that is a WordPress sort code, you need to activate Enable WordPress Shortcodes in Post Content option from Dashboard > Forums > Settings > Features Tab

So i have change all my video codes as

old code
<video controls=\"controls\" width=\"100%\" height=\"auto\">
new code
<video controls=\"controls\" width=\"auto\" height=\"350\">

and that works

But still remain the elite video shortcode that dont work in wpforo 1.99

https://www.vivrenu.com/forum-du-naturisme/reportages-emissions-tv/1974-08-04-ina-congres-naturiste/

and works in wpforo 1.96

https://test.vivrenu.com/forum-du-naturisme/reportages-emissions-tv/1974-08-04-ina-congres-naturiste/

and yes it is a wordpress video shortcode which is already activated in Dashboard > Forums > Settings > Features Tab

The issue seems not to come from shortcode as i can use other shortcodes like this https://fr.wordpress.org/plugins/photo-gallery/#description