Find the part of the sentence that contains an error:
That the policy omits provisions for backward compatibility (1) / is less troubling than the belief (2) / that all regional bodies will, without any pressure, (3) / complies with the central directive as issued (4).

The correct option is (4).

Explanation:
Let us analyze the sentence step-by-step to identify the grammatical error:

1. Part (1): "That the policy omits provisions for backward compatibility" - This forms a noun clause functioning as the subject of the sentence, which is grammatically correct.

2. Part (2): "is less troubling than the belief" - This contains the main verb ("is") agreeing with the singular clause subject, followed by a comparison ("less troubling than the belief"), which is correct.

3. Part (3): "that all regional bodies will, without any pressure," - Here, "that all regional bodies will..." introduces a subordinate clause. The subject within this subordinate clause is "all regional bodies", which is plural. The modal auxiliary verb "will" requires a base form of the verb after it.

4. Part (4): "complies with the central directive as issued." - The verb "complies" is singular, which creates a subject-verb agreement error with the plural subject "all regional bodies". Additionally, following the modal auxiliary "will" (from part 3), the verb must be in its base form "comply".

Correction:
Replace "complies" with "comply".
Correct sentence: "That the policy omits provisions for backward compatibility is less troubling than the belief that all regional bodies will, without any pressure, comply with the central directive as issued."

Therefore, the error lies in part (4).