Niantic has announced that they have disabled GO Battle League until further notice, as they’re investigating a serious exploit.

Note to Trainers Regarding GO Battle League Exploit

Trainers, we want to comment on the various “exploit” posts from the past two days and the underlying situation.

As a team, we believe there is a “contract of trust” in GO Battle League: you should always feel your knowledge and skill determine the outcome of your battles. Cheating directly attacks this trust contract, and we have zero tolerance for it.

Because of this zero tolerance policy and the current situation, we’ve disabled GO Battle League.

We’re equally serious about our policy of never commenting on the details of investigations into individual accounts. Here’s what we can share.

When a possible exploit is identified, we follow this process:

1. Analyze the issue - Data analysis is the most important work we do during this process. Rash action (i.e. no analysis) can solve the immediate issue; however, it leaves the door open for the exploit to return in the future.
2. Determine severity - Based on our analyses, we determine (a) the level of technical knowledge needed to abuse the exploit and (b) how badly the exploit harms the integrity of GO Battle League.
3. Mitigate accordingly

Based on the above outlined steps, the disabling of GO Battle League means we’ve arrived at the “mitigation” step of our process for the current situation. There is plenty of work happening behind the scenes, and we’ll re-enable GO Battle League once we’re confident the “trust contract” will be honored.

Source: https://niantic.helpshift.com/a/pokemon-go/?p=web&s=release-notes-known-issues&f=note-to-trainers-regarding-go-battle-league-exploit and https://twitter.com/NianticHelp/status/1271594784461778944