Client has a Cerbo installed with over 1GB free space. During tree trimming to improve solar yields, overhead fibre line was broken and internet outage occurred for a week. After restoring the link, we expected the missing and cached data to be uploaded but there is a gap.
We did not add an SD because the Cerbo has a lot of free space. 
I have not had hands on with the cerbo. But with the CCGX you can see the number of storred records on the device itself under the vrm portal submenu. Is there that option on the Cerbo? If not then it did not keep a log of the time period.
it probably ran out of data space during that time and earliest records were overwritten. Did you check to see if you ran out of space before you uploadeded and cleared the data ? You cant use the "free space" that it shows after you have emptied the entire stored contents. .
Its so cheap to get a xGB microSD, that its just easier to slot one in and not worry about it
Do you have the option to reboot after no connection set?
If so it's the same bug I reported in this thread. Although, no response from Victron.
I think regardless of if there is local space on the GX device they keep a maximum of 2 days without a SD card installed
