do you have an exception in your antivirus for scanning in the Thunderbird profile folder? My guess is Thunderbird is not finding anything because the store is locked by the antivirus while it scans for an age. If your say inbox is 4Gb in size. It might take it longer to scan it than the time between email fetches resulting is Thunderbird not having access to read and write the required file.

Thanks for your input Matt, but this only happens after Thunderbird is open a while, not a constant problem.

I've the same problem as discussed here and when deleting a file (as discussed in https://support.mozilla.org/en-US/questions/1468959).

• Topic occurs randomly
• Topic occurs since the last 2-3 TB updates
• Not in a specific folder, but can be anywhere, anytime
• I've my data nor my profiles in the cloud
• I've AVG running, but did not set any exceptions / exclusions
• Closing and opening TB solves the topic
• Size of my E:\Thunderbird\Profiles directory is ~17 GB
• I've ~500 filters defined over all accounts
• I'm running TB 128.3.2esr (64 bits), and about to download 128.3.3esr
• System: Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz, 64 bits, 8 GB RAM, Windows 10 Home, Build 19045.5011

I've the same problems as discussed in this thread and here (https://support.mozilla.org/en-US/questions/1468959)

• Topic occurs randomly in any directory, at any time
• I've no data nor my profile stored in the cloud, but on internal SSD
• I'm running AVG, but didn't define any exceptions / exclusions
• Closing and opening TB solves topic temporarely
• Topic is occuring since the last 2-3 TB updates
• My profile directory covering all accounts is ~17 GB
• I've ~500 filters defined over all accounts
• I'm running TB 128.3.2esr (64 bits)
• System: Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz, 8 GB RAM, 64 bits, Windows 10 Home, Build 19045.5011