question

This seems to be correct behavior. It deals with precision issues and with something called "tiny dist".

First, the precision issues. Take a look at this FlexScript:

string.fromNum(0.025, 20) // evaluates to 0.02500000000000000139

and

string.fromNum(0.25, 20) // evaluates to 0.25000000000000000000

The value 0.25 can be exactly represented as a double. The value 0.025 cannot.

The following logic happens:

1. The Source generates an item and attempts to send it to the conveyor.
2. The conveyor checks if there is enough room. If there were no precision issues (as is the case for the second conveyor) then the answer would always be yes, there is exactly enough space. However, for the first conveyor, the answer might be no, because of precision issues.
3. If the answer is no, the the source must schedule an event in the future for when there will be enough space. Again, precision is an issue. Technically, that event should be in zero time. But if it is in zero time, then we get into an infinite loop, because there still would not be enough room on the conveyor. The solution is that FlexSim adds enough time for a small gap, in addition to the entry space requirement. The small gap is a "tiny dist".
4. While the source waits for item to move a "tiny dist", it stays in the blocked state.

So one answer is to either increase the inter-arrival time or decrease the item size, so that you can never get a "false wait" due to precision errors.

In addition, the Snap Threshold setting on the Conveyor System contributes to the calculation of "tiny dist". If you make that value very small, you'll have less block time on the Source, since the extra gap will be smaller. But don't use a zero, or FlexSim will crash badly. The UI prohibits values smaller than 0.01 mm.