Yeah contest it.
Almost all temporary signage breaks the law and the tickets are difficult to enforce if they go to adjudication.
Have a google for “suspended parking bay”
Here is one example of what i found:
To whom it may concern
I wish to appeal against the penalty charge served upon me on the grounds that the council has failed in their statutory duty to sign the temporarily suspended bay in accordance with the law. The temporary suspension traffic sign used fails to comply with s.64 of the Road Traffic Regulation Act 1984 as it is neither prescribed by regulations nor authorised by the Secretary of State.
The DfT under Annex D2 in its Operational Guidance to Local Authorities gives clear and precise instruction;
PCNs may not be valid if they are issued where traffic signs and road markings
are incorrect or in poor condition. Representations demonstrating this should be
accepted.
I have demonstrated that the temporary suspension sign is incorrect (unless the council can prove to the contrary) and therefore I require the council to acknowledge their signing error and that this penalty charge be cancelled forthwith.
Yours with love, hugs and kisses.