Google Ads Weekly Spend Fluctuations Usually Related To Market Conditions Or Budget Changes
Briefly

Weekly spend fluctuations are typically due to changing market conditions (weather events, industry trends, etc.) and/or any recent budget changes in the campaign.
While the average weekly spend can fluctuate up/down with changing market conditions, campaigns won't exceed their monthly spend limit. We'll also notify advertisers around mid-month if your LSA campaign does exhaust its monthly budget.
You may also be more likely to experience this when the campaign has limited flexibility to meet and/or adjust to shifts in demand throughout the month.
Read at Search Engine Roundtable
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