Bloomberg reports on the matter
Saudi Arabia and Russia are said to be reluctant to extend output cuts without more compliance from the rest of the pact, citing people briefed on OPEC+ negotiations. Adding that there won't be a meeting tomorrow unless this problem is addressed.
A 10 June meeting will also now be dependent on the compliance issue being resolved, as Saudi Arabia and Russia are demanding better compliance to the agreement.
This should not come as a major surprise, considering that this has been the case in previous editions of the OPEC/OPEC+ deals. Not to mention, Russia themselves did not set a great precedent on this matter in the last version of the OPEC+ deal.
In any case, I made mention to this earlier in the week that OPEC only saw a 74% compliance across the board on the latest output cuts agreement - though that number is helped by Saudi Arabia pulling their weight on the matter.
That said, I would still expect this to be more of a threat than anything else. If the Saudis and Russia walk back the current agreement, oil prices may feel quite a pinch in the coming days/weeks.
Right now, oil has fallen down to $36.60 from around $37.40 prior to the headlines.