If the command "/scoreboard players add" is run too quickly, it will glitch and change a players count for an objective into a very high negative number

Scoreboards can only hold numbers to a certain size limit (negative and positive). If you surpass the limit, the number is inverted. This is intentional, but it could be changed so the number stops increasing / decreasing instead.

Thank you for your report!

However, this issue has been closed as Working as Intended.

This behavior is consistent between Bedrock Edition and Java Edition.

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