Enduring Bondwarden
I had two Enduring Bondwardens. One had 2 +1/+1 counters and the other had none. I blocked a 3/2 creature with the 2/3 warden and after it died I assigned its counters to the 0/1 warden. However when it resolved it had 4 +1/+1 counters instead of 2. It think it picked up another random counter later in the game. It was early in the game, I don't think I had any other cards out except maybe Invasion of Gobakahn unflipped.
Android
Extra counters when transferring from one warden to another.
Only counters the first warden had should be transferred to the second.
Sorry, I wasn't able to take a screenshot.

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Effigy#94738 commented
Similar thing happened to me with Enduring Bondwarden putting a counter on an Iron Apprentice, which then died that turn. It added 4 counters to the target instead of 2.
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[Deleted User] commented
The extra abilities a creature gains from Backup abilities are only for that turn.
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h4z3fr0g#78685 commented
When Enduring Bondwarden enters the battlefield, if a creature other than Enduring Bondwarden is targeted, that creature gains a +1/+1 counter and the rules text "When this creature dies, put its counters on target creature you control". However, when the targeted creature dies, this rules text does not trigger, so the counters are not redistributed.
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ChaoticLapras#37181 commented
Similar bug with having 2 wardens out, sacrifice one them with Corrupted Conviction that had both counters on it and moved the counters to Gitaxian Mindstinger, instead of receiving the proper 2 counters it received 4 counter instead.
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jnf630#49396 commented
This just occurred for me as well. I'm playing on my Windows PC. I didn't get a screenshot either.
Opponent had an Enduring Bondwarden with 3 +1/+1 counters on it, it died in combat, and they chose to place the counters on the other Enduring Bondwarden they had in play (which had no counters). It appeared to trigger and add to the stack twice and next thing I know my opponent has an Enduring Bondwarden with 6 +1/+1 counters on it.
I do have the game logs.