Same problem. This is a regression.
┌────────────────────┐
│ Thunderbolt -> │ ┌─────────┐ ┌────────────┐
┌─▶│DisplayPort adapter │───▶│DP cable │──▶│Dell P2715Q │
┌───────────┐ │ └────────────────────┘ └─────────┘ └────────────┘
│ MacBook │─┤
└───────────┘ │ ┌────────────────────┐
│ │ Thunderbolt -> │ ┌─────────┐ ┌────────────┐
└─▶│DisplayPort adapter │───▶│DP cable │──▶│Dell P2715Q │
└────────────────────┘ └─────────┘ └────────────┘
I previously used a MacBookPro13,2 and macOS 11.6. The bug was not present on that machine. Application windows would reliably hold their positions across both monitors after wake from sleep.
I recently replaced the MacBookPro13,2 with a MacBookPro18,3 (2021, 14'', M1 Pro) and macOS 12.1 Nothing else was changed. Same monitors. Same cables. Same adapters. The bug is now reliably reproducible.
On wake from sleep, application windows always move to the monitor with the Mac menu bar and dock. Electrical connections between the devices in the diagram above are never disturbed during sleep.