I had teleported from an overworld portal that led to a Piglin Bastion, went upstairs, and found my armor stands all empty. I had complete sets of leather, gold, iron, chainmail, diamond and netherite, so this is devastating.

Correction 9-29-2021 The armor stands were also gone, as well as the armor.

I'm not sure if this is related, but I had made a grandfather clock that used an armor stand as part of a pendulum. The armor stand that was inside the clock, and the shoes the armor stand was wearing, are gone. The grandfather clock was from a YouTube Tutorial from 4/28/2018 by Biggs87x and used pistons to place glass around the bottom of the armor stand.

I am a single player, not even signed up for Switch online anymore. I don't know anyone else who plays Minecraft. 

I've attached a photo of the armor stands with the armor on them that I had posted to my blog "An Old Lady Does Minecraft". Now the stands are there, but nothing is on them.

seed is 1233655356.  I had explored extensively and had recently gotten a message that maybe I should get rid of some stuff but I had already gotten rid of my last Minecraft world. 

This is a standard Switch with an additional SIM card. I'm on cable.

 I've had a series of name-tagged villagers and pets de-spawn and figured that that was because I am often far from base - but I've never had anything static disappear before (that I noticed).

After reading other issues I checked and all the paintings in my base are also gone, but not the item frames. 

I'm hoping that you can offer some advice on how I can avoid this kind of loss in the future.

Added 9-29-2021  There were two fairly close Overworld portals - 2091 73 -3605 and 2773 63 -3592.  Both end up at 342N 60N -459N, I entered the first OW portal but was returned to the second one. I teleported back to 120 64 -24 from 2091 73 -3605.