I believe, China want to engage Singapore at strategic level - and want Singapore to open a dialogue with China on Taiwan issue.
Singapore meanwhile want to engage HK - and let legal process take its course - on why the Terrex is seized, under what infringement.
Strategic level should be engaged separately - not under the pretext where Terrex is seized - and negotiation take place under "hostage situation".
This position is the correct posture.
China's perception of Singapore: 4 areas of misunderstanding
What China misunderstands about Singapore is that: Singapore is not a Chinese country despite having a majority-Chinese population; Singapore values a united Asean; Singapore is not a US ally but wants to be friends with all major powers; and Singapore has the world view of a small country.
ASSET AND LIABILITY
SINGAPORE'S COMMITMENT TO ASEAN
RELATIONS WITH MAJOR POWERS
DIFFERENT WORLD VIEWS
26 YEARS OF DIPLOMATIC TIES