A (hopefully) thorough timeline and facts about October 20th - Belfast - and things that happened around that time. Take what you want from them.
(all timestamps are BST unless otherwise said - go by the timestamps in the text aka the written ones)

So let’s start with some numbers: in their whole career as a boyband, they did 226 shows not one was canceled. All of the boys were sick at some point. There were broken bones, flu, asthma, other things, and they still performed. Every. Single. Show.
UAN 54
TMH 123
WWA 69
OTRA 80

Except for Belfast. 
Now let’s dive into it. To understand the whole situation in Belfast it’s important to look at a few days before & after and look at all the coincidences that happened during that time:

For reference later: Perfect (the audio) was released 16th Oct

OCT 20th
The day starts with rumors that Perfect the MV will be released and some screenshots start popping up online (of the mv)

During the day there were some scheduled interviews that brought more confusion into the mix with the information that was given to those reporters:

The reporters were told that N (not Liam) was sick.
(afternoon) interview with N was supposed to happen - but N was sick
5:30pm interview with Louis happens (w/Stephen Nolan) he said Louis was looking ok, he was told Harry’s foot was in a cast and that N was sick

6:41pm Sarah Clarke posts how she did an interview with only Louis https://twitter.com/sarahclarke_utv/status/656525557010706432?s=20

so these all happened a few hours before the show and no one has said anything about Liam not feeling ok, N is supposedly sick, but now it gets even more interesting.

7:30pm (2:30pm est) - Style magazine publishes a story about Louis becoming a father to a baby girl.

(the interview gets taken down but fans screenshot it and the cache for the link - credits to https://bulletprooflarry.tumblr.com/post/131571470371/saracha33-beccasafan-oh-my-god-one I took the ss from there I couldn't find mine on icloud)

And another interesting article gets published later on that night:
around 11:00pm an article gets published by the Sun (notoriously known for pushing S agenda) that Louis is to be a judge on x-factor. This will proceed to not happen. https://www.thesun.co.uk/archives/news/45424/cowell-wants-a-newy-louis/

So what happened to the concert:
Jamie Lawson who was the opening act for the show in Belfast performs.
After that - Jim Clarke (Aiken PR - they did PR for the promoter of the show comes on stage about an hour after One Direction was supposed to start singing and reads:

“Unfortunately, the show tonight has been canceled, as Liam has been taken ill. And while it is not serious, he is unable to perform tonight. A further statement will be made in the morning.” (Link to the video of him reading the announcement https://bulletprooflarry.tumblr.com/post/131573297246/knightchanges-xx)

After that fans are in shock and no official statements are made. They boys tweet in the following order:
10:10pm Harry
10:17pm Louis
11:18pm Niall
1:21pm (Oct 21st!) Liam

Also, that night while the whole fandom was in a panic we get a tweet from Louis tweeting out the link to the video for Perfect (but that was probably scheduled since it was tweeted at midnight straight and from the twitter web app)

(At night - that same night the concert was supposed to happen) N is pictured on a crew member’s FB post out somewhere (not looking sick )

In the early hours on the 21st, 1am BST (8pm EST 20th) an interview Simon did for GMA is published in People Magazine. Simon talks about giving parenting advice to Louis and how he can sympathize with his situation. (This interview airs on 22nd officially)

Then we get to the Home part:
A special perfect EP is put on Spotify where Home was one of the songs (which didn’t make any sense since it was just different versions of Perfect and Home randomly thrown in there)
And we have Louis tweeting the lyrics to the song and the

In the following days, the boys did a series of very odd interviews where they didn’t talk much about what happened that night and blamed what happened to Liam on diarrhea. Later in 2016, Liam would say in an interview that it had to do with his anxiety.

The canceled concert was rescheduled for the next Friday 23rd (2 days after) and they ended up performing normally on Oct 21st & Oct 22nd.

And to bring in the cherry on top - on Oct 21st rbb and sbb start their 5-day countdown on their twitter. (that's a whole other thread).

So what we know happened is Louis did interviews about him becoming a father that day and I will let you judge how he liked those interviews - I’ll leave a link here. That combined with the articles that came next was so very unusual.

After a day of those interviews, an untrue story in Style magazine being published about L and B welcoming their child, Simon being in the papers talking about Louis, rumors about x-factor and everyone saying N was sick, the concert gets canceled because apparently, Liam was sick

The boys tweet their apologies but no official statement gets made for 12h. Home gets leaked and we have Louis of all people tweeting about it. Niall is seen looking very healthy out with some friends that night. And rbb and sbb start their countdown on twitter

And before anyone comes with the "it's just a canceled concert" It's not just the concert being canceled - it's the whole 48h and everything that went on during them that seems weird. The excuses, the articles, the stories not adding up. A lot went down and it was a mess.

I think this thread should cover everything that happened in chronological order. I'll again give credit to http://bulletprooflarry.tumblr.com  and https://bulletprooflarry.tumblr.com/post/131571470371/saracha33-beccasafan-oh-my-god-one because I wouldn't have those screenshots to show you without them.
And if I messed up somewhere please correct me.

Have fun reading. This is me showing you the facts - I am not in the business of making anyone believe anything they don't want to. If you don't like what you see here just scroll past, ignore this and live in peace reading what you like