Here's the thing timing issues are either a lack of technique to play efficiently or the lack of internalisation skills of what is needed to count in time.
Telling someone how to count or giving them tips on how to count are pointless, they already know how to count. What they cannot understand, and therefore do, is the rhythm of counting. This is an internalisation skill that is done by training for those that lack the cognitive skills to do it, those that have it naturally do not need to train it, but better understand how to use it.
This has nothing to do with music, music is one of the applications we can use it for. From Golfers to athletes, to actors to secretary's , from reading a book to your work place, it all uses rhythm......or in its other form timing.
For this a metronome is needed ( or drum machine, or rhythm box ), but not a bass. Since the bass is the physical side,we need to work out where the fault is.
If after working with the metronome everything seems good, the we can move to the act of playing, without the metronome I may add.
If we find the problem here, then we have identified it is in the technique and therefore nothing to do with counting, so we can address the problem in specific ways.
If it was a case that the technique was fine, and we looked to the internalisation side and found the problem there, then again, we can address it in the same specific way. The first thing to do is identify the source of the problem, then address it....... it will either be a mental one or a physical one.
In the work place the syncing of such ideas is time and motion, and ideas like playing music to workers on an assembly line keeps them all in sync, they will tend to all work in sync to the music being played, rather than each owns individual body clock working against each other.
Also noted is, if the temp is faster then the output will raise as the workers will naturally work faster.
I always start with the mental side, look to that, then look to the physical with
anyone that presents timing problems to me, then make them aware of where the problem is. By understanding it they they lose the fear and anxiety of it and it develops into being second nature, which is all part of internalization.
The use of a metronome, drum machine, or rhythm machine is used to check and ingrain tempos and rhythm by listening to them first, count and understand what you are going to apply to it. When you have it, turn of the machine and play it. If need be repeat this. When you have it, play it once to the machine to check it.....do not keep playing over and over to the machine.
Those that do not have problems are free to play over and over to a machine because their focus is not the machine. This is the problem with trying to learn and work with a machine is that it becomes the focus, not the music, not the technique, but the machine. This can cause other problems that are nothing to do with playing to arise.
Now there may be a genetic link to a timing problem.
Speaking fluent is something we all can do, but those who stutter cannot.
They cannot time certain words so they lose the rhythm of their speech.
It may be a emotional response, look how many people cannot do public speaking. They are fine in everyday life, but give them a mike and as them to make a speech.....the results are sometimes all the things we see in players caused by anxiety.
These are just a few of the mental side thing that may or not be present, just as the physical side may have other things present such as a weakness brought on by injury or illness, maybe even a genetic condition get in the way.
The simplistic way to sort timing issues is to understand and learn the timing of what you are playing. So many people learn lyrics, chords, melodies etc, but just accept timing as what they hear over all. I have lost count of how many times I have been told its verse chorus, verse chorus, middle 8, solo, etc, and when I ask "how many bars" to any one of those elements they cannot tell me straight of......because they have never really thought of it. If you cannot tell me how many bars there are in the solo, then you do not understand the timing of the song. As I have said timing, tempo, and rhythm, is motion...it moves, so you have to understand the parameters of that movement.
If you hesitate, because of the mental or the physical side, then you will get out of time with the motion.
Music does not wait for you it flows own and it is your duty to understand and look after your own tempo and timing.........a drummer does not set the tempo or a timing, he just represents it, and he can represent it wrong.
Everyone in the band is responsible for tempo and timing, it does not belong to any one person.