Cyrillic wght: 100-400 | wdth: 100 | slnt: 0 | GRAD: -50 - +50 | opsz: 144

Here are my observations for opsz: 144 for weights 100 and 400 (I will follow with wght 900 next). Unless mentioned differently the comments apply to whole range of grad -50 - +50.
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wght: 100 | wdth: 100 | slnt: 0 | GRAD: -50 - +50 | opsz: 144

1. шщж - too wide
2. ПЦ - slightly too wide
3. Ж - could just a touch narrower
4. ШЩ - too wide
5. ф - too narrow
6. Ы - right stem rendering issue - appears too light or disappears, while in fact the weight is correct.
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wght: 400 | wdth: 100 | slnt: 0 | GRAD: -50 - +50 | opsz: 144

GRAD: -50 - +50

1. This starts in grad -50, but is most visible in grad 50. БВРЯЗЪЬ - seem pretty narrow in titlecase setting, while Д and especially Л give the opposite feeling. Since БВРЯЗ widths came from relation to Latin letterforms, maybe ДЛ could be narrowed?
Breve.cyr.case - slightly dark and could use more contrast
Breve.cyr - too wide and slightly dark - can use more contrast.
2. пн can be slightly wider. This starts in grad -50, but is most visible in grad 50.
3. Ф - appears wide
4. Ч - slightly too wide
5. б (grad 0-50) - can the tail be touch darker?
6. ШЩ - too wide
7. ПЦ - slightly too wide
8. ж - slightly dark
9. Д - left descender going a little further to the left in grad 0-50, than in grad -50.

Grad 50:

1. ИЙ appear a little darker in text than the rest
2. к - feels touch dark