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I was able to replicate mentioned issue on my cloned form. It seems that CSS style is not applied on other check box option.
I will escalate this issue to our developers. Once this issue is resolved we will inform you via this thread.
For now as possible workaround you can add one additional check box option "Other" and if that option is selected you can set conditional logic to show once additional text box field where your users will be able to enter "other" text.
Here is my demo form: https://form.jotform.com/60614799790974
Feel free to clone it.