Hey,
One of my customer just report me this problem, after a research, there is a kb for this https://www.veeam.com/kb4483

The problem is on the MS side 

Thanks - this looks like it could be the cause! When did your customer first see the increase? 

We also see this on multiple tenants. Especially last week.

Since last week like you, 26-27 March

I’m seeing an increase as well, but I’m also having issues viewing my buckets in Wasabi (possibly outage-type issue, I have a case open), but looking at my overall dashboard, I see an increase in my consumption over the past month as well.  However, this graph isn’t nearly as dramatic as what you’re seeing because most of my data is in VBR buckets and not for VB365 so may really temper the overall growth.  I’m guessing once I can view my individual buckets it may be more telling.

I’m seeing an increase as well, but I’m also having issues viewing my buckets in Wasabi (possibly outage-type issue, I have a case open), but looking at my overall dashboard, I see an increase in my consumption over the past month as well.  However, this graph isn’t nearly as dramatic as what you’re seeing because most of my data is in VBR buckets and not for VB365 so may really temper the overall growth.  I’m guessing once I can view my individual buckets it may be more telling.

 

Rather than checking the utilisation from the Wasabi bucket side, you could do the storage consumption report from Veeam - this is where my graphs are from 

Well, that was my next stop, but I do some reporting on my bucket sizes at the beginning of the month, so that’s where i had started anyway.  :-)  Also, support got back to me and I might have something blocking internally...so the hunt begins.

Update: 

Our incremental backups still appear to be significantly larger and therefore this does not appear to be the same behaviour as documented in https://www.veeam.com/kb4483
 

MS365 support have confirmed a fix has been implemented for this: 

As per product engineering team, a fix has been rolled out in Exchange Online backend to mitigate the impact.

Our backups seem to be back to normal, for now… 

Can you pls provide source for this fix.

Statement isn't mentioned in https://www.veeam.com/kb4483

I had a case open with Microsoft 

• Case #: 2404100050001099

Looking at https://www.veeam.com/kb4483, there is the following statement:

Due to changes we Microsoft] are making to optimize search and compatibility functionality within our service, this action led to re-indexing for some of our customers' data. The re-indexing is not indicative of a change to fields material to our BCDR and storage partners, so we will be working on a change to minimize the re-indexing that is prompting another backup of customer data. We made changes over the weekend of 2024-04-20] that should pause the unexpected behavior and those changes will be in place until Microsoft and our partners are able to make longer term enhancements to avoid future issues from taking place.
Thank you for your patience.

This has happened again… 

https://www.veeam.com/kb4483