adding some small delays fixes the artifacts for me:

import time

wait_ms(25)
touch_button0.set_hidden(True)
wait_ms(25)
lcd.circle(130, 100, 90, fillcolor=0xffff66)

Thanks
Felix

from m5stack import *
from m5stack_ui import *
from uiflow import *

screen = M5Screen()
screen.clean_screen()
screen.set_screen_bg_color(0x000000)

touch_button0 = M5Btn(text='Button', x=22, y=86, w=70, h=30, bg_c=0xFFFFFF, text_c=0x000000, font=FONT_MONT_14, parent=None)
touch_button1 = M5Btn(text='Button', x=117, y=86, w=70, h=30, bg_c=0xFFFFFF, text_c=0x000000, font=FONT_MONT_14, parent=None)
touch_button2 = M5Btn(text='Button', x=213, y=86, w=70, h=30, bg_c=0xFFFFFF, text_c=0x000000, font=FONT_MONT_14, parent=None)
touch_button0.set_hidden(True)
lcd.circle(130, 100, 90, fillcolor=0xffff66)

if you run the code in UIflow, it shows different results but it consistently shows the "artifact" of the hidden button.

how do you get rid of the hidden button artifact?

Basically, I think my UIFlow project became too complex for the system to handle. So, I rewrote everything in micropython. The code runs very well, no more randomness.

Github repository of my MQTT Thermostat running on Core2 is here.

It's pretty cool. The thermostat supports various modes: off/auto/manual/heat/cool/fan. You can specify minimum cycle duration as well as set swing mode parameters. It automatically gets discovered by Home Assistant. You can set thermostat mode and target temperature in Home Assistant and they will automatically get reflected on the Core2 display.

It currently relies on the ENVII module for temperature reading, and requires a WIFI connection and an active MQTT broker. I haven't had time to implement error handling, so if something goes wrong, it might be non-obvious to figure out why. More work to be done.

2/ Arduino would give you more control vs. uiFlow where you rely on blocks to do the work (coding) for you. If you don't know what's going on "under the covers" of the blocks (due to lack of documentation, uiFlow not being open source, etc.), it's hard to debug the corner-case issues. The downside to Arduino is that UI development is harder (you can't just drag/drop elements to the screen like with uiFlow). Also, you need to be a good programmer and understand all the syntax to make something work :-)

3/ Not quite sure yet. I'll give your program a try to see if I can figure anything out. Can you please also post the images that go above buttons A, B, and C? I already have HA set up and ready to go.