ZMS Data Loss — ATE ID 0x1A80 Overwritten

Question

Environment: nRF54 SDK v3.0.0, Zephyr Memory Storage (ZMS) 
 
 Config: 4 sectors × 4KB = 16 KB partition 
 
 Record IDs involved: 0x1A80 (SRAP data, 253 bytes), 0x1A21 (pairing info, 408 bytes) 
 
 Observed behavior: Data is correct after power-on. After some runtime, 0x1A80 reads back corrupted data. 
 Flash Dump — Sector 0 ATE Entries (sector tail) 
 ATEs at the end of the first 4KB sector, ordered from newest to oldest (ZMS writes ATEs backward from the sector end):

Address Content (hex) Interpretation
------- ------------------------------------------------------------------- -------------------------------
4080 54 2E FF FF FF FF FF FF 00 00 00 00 01 42 00 00 Empty ATE (cycle=0x2E)
4064 67 2D 00 00 FF FF FF FF A0 0D 00 00 FF FF FF FF ZMS_HEAD_ID (cycle=0x2D, offset=3488)
4048 D0 2E FD 00 80 1A 00 00 00 00 00 00 00 00 00 00 → ID=0x1A80, len=253, **offset=0**, cycle=0x2E
4032 C7 2E 04 00 05 1A 00 00 01 00 00 00 00 00 00 00 → ID=0x1A05, len=4 (inline data)
4016 F1 2E 00 00 FF FF FF FF 00 01 00 00 FF FF FF FF ZMS_HEAD_ID (cycle=0x2E, **offset=256**)
4000 A1 2E 98 01 21 1A 00 00 00 00 00 00 00 00 00 00 → ID=0x1A21, len=408, **offset=0**, cycle=0x2E

ATE structure (16 bytes): crc8(1) + cycle_cnt(1) + len(2) + id(4) + data/offset(8) — little-endian. 
 Observations

Both 0x1A80 and 0x1A21 have offset=0 — both point to sector base address 0 as their data location. Since 0x1A21 (408 bytes) was written after 0x1A80 (253 bytes), 0x1A21's data physically overwrites 0x1A80's data at offset 0.

The ZMS_HEAD_ID entry at offset 4016 records offset=256 — this is a GC-done marker written when data_wra was at position 256 within the sector. However, the subsequent 0x1A21 ATE at offset 4000 records offset=0 , meaning data_wra was reset from 256 back to 0 between these two writes.

The ZMS_HEAD_ID at offset 4064 has cycle=0x2D (different from the 0x2E cycle of all other entries) — this is a residual entry from a previous sector cycle that was not fully erased.

In the second sector (lines 258-513 of the dump), the sector has been GC'd/erased. Although a 0x1A80 ATE entry still exists at this location:

08 2D FD 00 80 1A 00 00 00 00 00 00 00 00 00 00 → ID=0x1A80, len=253, **offset=0**, cycle=0x2D

The actual data at the offset it points to (offset 0 of this sector) does not contain the real 0x1A80 payload — the data at that address belongs to a different record, confirming the data was overwritten there as well. 
 
 Question 
 Could you please help us understand what conditions in ZMS could cause the data_wra pointer to be reset back to 0 after a GC cycle has already advanced it (to 256 in this case), resulting in two different records pointing to the same data offset and overwriting each other? No power loss or system reset occurred during this failure window. 
 
 20260509.log