Unfortunately all at the beginning shield buffs are subject to only lasting 3 rounds, unless stated otherwise. Shields generated during the battle last indefinitely unless stated otherwise.

It would be great if there was someone dedicated to talent description and increase standardisation.

It should be mentioned that the shields will apply for only 3 rounds. It only removes from 2 units not all 4. So that's another thing thats weird. Unless you apply the mains mystery to add a bonus shield and the same unit keeps reciving shields it may only remove the only first round shields.

I am pretty sure you are not looking closely enough but to clear things up passives like Earth main Boulder Jutsu and Gaara's Defender of the Land of wind first part both do not have descriptions mentioning that they only last for 3 rounds.

Other Examples: Temari - Defender of Hidden Sand, Ao - Defender of Hidden Mist, Akatsuchi - Defender of Hidden Stone, Mabui - Defender of Hidden Cloud ect.

Secondly any shields that are generated outside the said type are permanent unless stated otherwise.
This include most mystery type shields like Kurenai - Mirror Guarding and Gakido - Absorption. Only one mystery type shield that disappears that I know of is Jugo - Living Wall Fist

Others that generate shields as standard or secondary passives are also permanent
Example of standard: Earth Main and Akatsuchi - Petrifying Jutsu

Note these passives types have much different structure than the passives you are noting
Example of secondary passives: Gaara - Defender of the Land of Wind second part, Kidomaru - malleable metal Armour, Gaara - Sand Hell second part

Yeah, I can understand that. I was just confused at the moment. Thank you for the clarification.