Combat
I think you are right - I read some time ago that Hitler was scared of a return to Gas Warfare and he had been scared by the experience during WW1 - friends and comrades were victims in the Germany Army.
He did have his troops prepared for Gas attacks and always feared the French would use Gas as a last resort to fight the Germans - I will go back and try to find those accounts. It was interesting to me - because it showed a little human side of Hitler in his conduct of the War. He was still mad & a monster - but, this showed something IMHO.
Ron
If he had an aversion to gas through personal experience, that only indicates further his depravity towards the millions of innocents he did gas!
I suspect it had more to do with avoiding retatilation in kind or lack of effectiveness in real-world battlefields
found this in wilkipedia (where else

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In the Geneva Gas Protocol of the Third Geneva Convention, signed in 1925, the signatory nations agreed not to use poison gas in the future, stating "the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices, has been justly condemned by the general opinion of the civilised world."[40]
Nevertheless, precautions were taken in World War II. In both Axis and Allied nations, children in school were taught to wear gas masks in case of gas attack. Italy did use poison gas against Ethiopia in 1935 and 1936, and Empire of Japan used gas against China in 1941. Germany developed the poison gases tabun, sarin, and soman during the war, and, infamously, used Zyklon B in Nazi extermination camps. Neither Germany nor the Allied nations used any of their war gases in combat, despite maintaining large stockpiles and occasional calls for their use,[41] possibly heeding warnings of awful retaliation.
Although all major combatants stockpiled chemical weapons during the Second World War, the only reports of its use in the conflict were the Japanese use of relatively small amounts of mustard gas and lewisite in China,[27][28] and very rare occurrences in Europe (for example some sulfur mustard bombs were dropped on Warsaw on 3 September 1939, which Germany acknowledged in 1942 but indicated that it had been accidental).[24] Mustard gas was the agent of choice, with the British stockpiling 40,719 tons, the Russians 77,400 tons, the Americans over 87,000 tons and the Germans 27,597 tons.[24]
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The mustard gas with which the British hoped to repel an invasion of the United Kingdom in 1940 was never needed,[29] and a fear that the Allies also had nerve agents[30] (in fact the Allies were not aware of them until the discovery of German stockpiles) prevented their deployment by Germany.