Import of goods from 1s, why can "Temporary tables deleted" loop?

Question

1C-Bitrix

Import is divided into 4 folders, each contains files import.xml, offers.xml, prices.xml, rests.xml
Folder No. 1 is loaded completely, then import.xml is loaded from folder No. 2 and when it comes to offers.xml, the following is visible picture


And so it can go until blue in the face, after some manipulations, in the log
on 12/17/2020 9:11:58--Receiving data from the server: An empty server response was received.
2020/12/17 09:11:58--offers___2dff4661-f90a-449a-b700-281a421105a3.xml: Failed to get the current exchange process status. Exchange data sent but not uploaded.

Accordingly, the offers.xml file from folder No. 2 is not processed, after that the import continues and all other files from folder No. 2, 3, 4 are loaded correctly.

Import settings in Bitrix:
Interval of one step in seconds (0 - download in one step): 45
Size of the one-time downloaded part of the file (in bytes): 15000 (this, by the way, is very confusing ~ 15Kb)

In 1C:
step in seconds: 300

There are two more questions from this:
1 .very embarrassing that the size of the downloaded part of the file is ~ 15Kb, is it very small? everywhere they write that it is necessary to calculate the type in an experimental way for each site, but this is not option
2. Should the step in the BUS coincide with the step in 1C?