EOS R exposure varies between shots of same subject

[Wahyu]

I’m taking pictures with eos r, I’m press the shutter several times for 1 object (model) with same setting. but why the exposure of each image was different? especially if using strobist

[p4pictures]

What camera exposure mode are you using? Also you mentioned using strobist, does that mean you are using a Speedlite too? If so what mode is the Speedlite working? 

The way to ensure 100% exposure consistency from shot to shot is use manual exposure mode M woth a fixed ISO, and if using flash then you also need to use M mode and set the power level on the flash. 

[Wahyu]

both of camera exposure & speedlite in manual mode.and i’m using fixed ISO speed too

[p4pictures]

Are you shooting quickly? If the Speedlite has not fully charged it may not be able to deliver the set power. Canon Speedlites usually fire even if they are partly recharged. Many of the less expensive independent flashes do not fire unless fully charged. 

Can you share an example of a few images to help me work out what is going on? 

[Wahyu]

I don’t think so sir, i take 2 scnd at least, here the examples