I also have a rather bad F experience with SQ.
From CDG to SIN, MANY things went wrong.

1. An used sock from the previous passenger was on the ottoman under a sealed blanket.

2. Side container was full of garbage.

-> cabin crew moved me to another suite (only myself and 1 other passenger on this flight)

3. A plastic wrapper (may be from the slippers) was in the side container. Cabin crew Came to apologise again. And offer to move me again, I turned it down, as it wasn't a big deal, not like the first suite with an used sock.

4. The book the cook meal, rice was half cooked.
They offered me to pick another main from the inflight menu, which I refused. Have enough food.
Later she told me the other passenger also left the rice almost untouched. What a coincidence, both passengers ordered the same book the cook.

5. Headphone issue, there was a background noice, even a new pair was given. So may be a seat issue, changed seat again.

At the end, they told me they would file an Incident report. Before arriving SIN, I was given $200 Krishop voucher and a pair of SQ bear.

IFM didn't come to apologise and not much interaction with me (try to avoid me?)

So I filed an online complain, not asking any compensation. For the first incident, really a hygiene issue. No reply after a few days. So send them an email, got a generic reply.

So far this was my worst F experience of all airlines.
Ironically, my outbound flight SIN-CDG was my best experience on all F to date. It was so memorable and the cabin crew really made me feel like a VIP. The services was beyond excellent. I also wrote this in both my online complain and email.